Yes a J can file an extension of status to a B however there are a couple of different issues raised in your question and I would recommend...

I am from Nepal

Four years and nine months from the date your green card was issued to you. I would recommend working with an immigration attorney to help you file...

?WHAT'S THE REASON FOR INADMISSIBILITY AFTER BEING DEPORTED FOR 5 YEARS AND I BEEN APPROVED FOR A IR5 VISA?

I would strongly recommend working with an immigration attorney to do this. Case specific advice cannot be provided here. The grounds of...

N-400 Denial possibility and consequences?

In order to get proper case specific advice you need to consult with an immigration attorney but generally speaking you need to have the requisite...

My boyfriend applied for a J-1 visa to come to the US. Can he and I take the same flight?

Only generalized immigration advice can be given here and generally speaking the J is a non immigrant visa (ie will return home at the end of your...

Asylum case pending for 5 years! no interview yet

Unfortunately all the old asylum cases now have to wait until they start processing old cases again

Did I violate the 30/60/90 rule for i-485 application ?

From the information provided it looks like you did violate the rule so fraud will likely be presumed.

Reapplying for a US tourist visa with an arrest?

I would recommend meeting with an attorney for proper case specific advise. Generally speaking yes a violation of a drug law in or outside the US...

I am planning to apply for a name change in naturalisation process?

USCIS will not give you a new passport after the name change you will have to change the passport and SSN separately.

Can I file for i485 if some original documents is missing?

Only general advice can be given on these forums, if you want case specific advice you need to see an attorney who can review all your documents....