Does certified eb2 PERM require to downgrading eb2 to eb3? and missing old attorney signature and employers? can I use that

Yes you need the copy of the EB2 Labor to down grade to EB3

L1 (Company A) to H1 COS (Company B) approved with I94 attached while i was out of country ?

Get your form I-94 online to confirm what your last/current status is.

Can I add a travel document request to my existing I 485 green card application?

It is not too late to add the application for Advance Parole.

If you weren't seen doing that and there were no traffic cameras, then no.

Filed I130 for alien relative in mexico? And we recieved a notice of approval but nothing arrived in mail?

You can call USCIS customer service to follow up and perhaps, put in a service request. The phone number is on their website.

Depends on the circumstances surrounding the dismissal. Consider a private consultation with an experienced attorney.

H1B extension on previous employer's I140?

More information is needed to properly answer your question. Consider a private consultation with an experienced attorney.

How to bring a child in USA, of a Valid Green Card holder Mother who just born in abroad?

You can apply for admission using the documents that prove the relationship. Contact the local US embassy for further directions.

https://www.uscis.gov/i-485Checklist

Im Out of status- Can I travel in flight from Texas to california?

Yes you can. However, you can be arrested if you run into ICE officials.