I was illegal in one country which was not US and I want to Apply for K1 Visa how much percents chances of refusals????

I think your illegal stay in the other country should not be a problem unless you had criminal or other issues there.

Will a I-601 waiver be needed in my case? If so, what are the chances that it will be approved?

Based on your information it appears he would need a 601 waiver

Can i continue to work on H1B with employer B, if L1 extension applied by employer A gets approved after moving to H1B with COS?

I agree with Mr. Capriotti

Re enter usa with old visa and new i20?

I agree

How can I get an F1 visa if my status change (B2 to F1) just got approved (e-filing the I-539)?

I agree with Mr. Calehr

What should I do if my Stem Extension gets Denied?

I agree with my colleagues

I have TB scars showing in my X-ray , But i don`t have active TB . Will it effect My K1 Visa ..?

I agree with my colleagues answers

French and looking for a work permit in the US

I agree with Mr. Capriotti

I agre with my colleagues

I received an RFE(Request of Evidence) on my OPT STEM extension, its been 15 days still NO RFE in mail, any suggestions?

Your question is confusing