How to get deportation record and what to do to get it ?

File a request for his file under the FOIA.

My wife was refused back to the US because she over stayed in the US. i am a US citizen and she is a canadian.

You can petition her for an immigrant visas and she can file any waivers that she probably now needs. Consult with an immigration attorney.

I am on H1B visa & need to change a job. My current company started application for green card. Can I change my job?

You could, but it is likely that your current company would withdraw the visa petition.

Can someone who is a citizen of united states who has a felony sponsor their spouse?

This depends on the nature of the felony. Certain convictions for domestic violence and/or sexual assault-type crimes can bar a petition.

To extend I 94 or file new petition?

L-1 stay is generally limited to the validity dates of the petition.

Can you suggest your ideas

Canada has its own rules governing admission. Consult with a Canadian immigration attorney.

This inquiry makes no sense. K-1 visa admittee has already done a medical exam and should not need to do a new one when filing an I-485. I-485A...

You can still obtain a record of your correct/most recent I-94 from the CBP. Visit their website.

My son (UK, 22) has his Green Card but has been absent from US for 5 yrs. After visiting recently he wants to return, can he?

Your son has abandoned his green card. You may petition him to acquire a new one, however, he will have to wait several years.

Your cousin should consult with an immigration attorney himself when he arrives in the US.