Do the needful means do that which is needed. It's mainly used in formal written communication, especially when dealing with bureaucracy. It can be preceded by the words “kindly” or “please.” Ideally, it should follow an explanation of a problem that needs to be fixed or a request that is being made.

Is the needful offensive?

Some computer tasks work but our other office has not. Please do the needful." To directly answer the OP's question, it is exceptionally rude. It is presumptuous in telling rather than asking, and carries a condescending tone.

Do you need oblige and needful?

Please do the needful and oblige. I have seen this sentence frequently used( especially in the Indian subcontinent) in letters/notes or memos from senior staff to junior staff. It means "oblige"(=perform) the instructions/orders given in the letter/note/etc.