I was asked this question recently- Are you wearing anything underneath your shirt?. So, I am wondering if it's possible to use under instead of underneath in the above sentence?
Under is used when something is directly under another object.
Underneath is often used to say that something is covered by another thing.
Therefore, referring to the question : "Are you wearing anything underneath your shirt?", that person is probably referring to the thing you are wearing inside, instead of "under" which the person would refer to the thing you wear at the lower part of you shirt.