A: That was Sherry. She wants me to go to Hong Kong next month.
B: Why don't you?
A: I don't know whether I should go or not.
B: I think you should, but, it's up to you, of course. Do whatever you want.
★ Why don't you?的原形是Why don't you go?也就是省略了go一词。Why don't you ~?「你何不~？」是提供意见或劝说时的实用句型。
★ Do whatever you want.「你想做什么就去做。」