Laid off on I-485 AOS AC21

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Question 1: What are the documents I need to keep handy from my original/current  green card employer for future immigration purposes? ( For instance : Any letter of recommendation , Proof of employment etc)
Answer: Copies of PERM ETA 9089 (or other evidence showing the job description used for your PERM application); and a copy of the I-140 approval. 

Question 2: When I move to a new employer what immigration related support do I need to ask my new employer apart from asking to file I-485 J ?
Answer: Just the Supplement J.