Wynn Liang

He could loose his citizenship if they decide to take it away for the reason he is in jail
 
and of course he has to apply for this visa not the immigrant
 
added to that are issues like the following
 
The fact that the American petitioner was in jail added a significant layer of complexity to the case. For example, the petitioner required permission from the prison to have his passport sized photos taken. Additionally, the prison social worker was very concerned that the American petitioner was somehow taking advantage of the foreign fiancee – it was like IMBRA on steroids. 

Hello, If you read the instructions, it ask you to select only one box.  And there are only three choices. When you stated that he was born in the United states of America in L.A then 40.a. which is birth in the United States is the answer. Anyways, Why dont you downlaod the form, print it and send it to your fiance' or ask him to go online and download the form, print, and have him asnwer or fill up the form since he is the applicant.

Yes.
 
Don't fill the form online or on the phone. The best is download the form on a computer and open the file with acrobat reader and fill in. 

he was born in Los Angeles, he has a certificate of live birth, are they the same?can i use the certificate number on the certificate of live birth?

Greetings!
If he was born in Los Angeles and have a live birth then why are you making it difficult?
Just check or choose 40.a born in the United States period ( only check one).
" YOUR CITIZENSHIP INFORMATION"
" YOU ARE A US CITIZEN THROUGH (SELECT ONLY ONE BOX):
40.a.___ BIRTH IN THE UNITED STATES.
40.b.___ NATURALIZATION.
40.c.___ U.S. CITIZEN PARENTS.

he was in jail because of domestic violence before, now is because of the probation violation.

You use the passport number as the passport number.   You don't use the passport number as a number for anything else.

im okay with my fiance's case, are they gonna grill much about it? or don't give us approval?

he was in jail because of domestic violence before, now is because of the probation violation.

Absolutely

The jail might or might not let him download 
I suggest that you fill out the forms with the help of his family members.   Or his help since he seems to have to a phone.  Then email the forms one of his family members to print out and take to the jail during visiting hours.  The jail might or might now allow the visitor to meet with your fiancé with pens (pens are sharp). Some  jails won’t let papers be passed to your fiancé.  If so, your fiancé will have to hire a lawyer to meet your fiancé with the papers to sign. A lawyer is always able to to have physical contact with a client in jail.  
 
 
You will need a joint sponsor.  It has to be someone living in the USA who is a citizen or lawful permanent resident.  
 
 
The lack of income is handled by a joint sponsor.  
 
Depending on the crime he might or might not be allowed to petition you.  For example if his crime was assaulting a spouse, he is not likely to be approved.  
 
There is nothing you can do about his criminal record.  

The first part of the journey is tbe petition and the responsibility of the USC,  he needs to figure out how to do the forms.

Also depends on what he's in jail for. Some crimes may make him ineligible to petition a fiancée.

Perhaps wait until he's out of jail and has a job before petitioning you?

Domestic Violence is taken very seriously.

One of the documents the US embassy provided to my wife upon her visa issuance was a pamphlet about domestic violence. I'd assume the CO will grill much about it during your interview even if uscis approves the petition.

he was in jail because of domestic violence before, now is because of the probation violation.

Agree with @milimelo.  Wait until he is out of jail to start the process.   In the meantime, study and learn the information in the K-1 guide here:
 
 

Unfortunately I have to agree with the other posters that unless you have a friend or relative you trust implicitly over in the us who can help get the documents together, who has visiting rights, and if the prison allows papers and a pen to be passed to your fiancé then it may be easier to have him petition once he gets out. 

If I followed your original post dates then you will still have time to gather documents before the having met once within the two years preceding application is up. 
 
I realise this isn’t what you want to hear but this process is something most of us on here wouldn’t want to rely on someone else not to mess up - why most of us use this site rather than lawyers. 

Even if he did petition you now, there is no way you would be here in 8 months.
 
And I agree with the others.   Wait until he gets out.   He has no way to support an immigrant from prison.

What’s he in jail for?  It isn’t domestic violence or trafficking is it?

he was in jail because of domestic violence before, now is because of the probation violation.

That’s fine, but then there is the issue of sponsorship.   Even with a joint sponsor, the petitioner would have no potential income from prison.   I think a public charge inadmissibility would be likely.

He gets out in 8 months. The rate things are going he will be out long before the interview and like everyone else who doesn't work or doesn't make enough they get joint sponsor. 

This is exactly the case. Getting the forms signed and copies of everything can be handled by a family member you trust with access to the forms. If you can get a family member with visiting privileges to take the paperwork to him to sign in less he is in supermax/ death row/ segregation lock-up the visitor can bring a pen for him to sign the forms with without an issue. If he is in one of the aforementioned situations ( I doubt it, because you said he is going to be out in 8 months) so getting the forms signed and mailed isn't going to be a issue. I don't think it would be that difficult to file everything as it is going to take 8-10 months to get to NOA 2 more than likely, and if he has a joint sponsor lined up, that will cover the I-134 that needs to be filled out for the interview.  As others have said, make sure his convicted offense isn't a disqualifying one, and make sure to disclose it obviously when you fill out the petition.
It's up to you if you want to try and get a jump on the process, or as others suggested wait until he is released and begin the process.