'Shall we talk later', can we put a question mark after this?

Solution 1:

This is a direct question, so you absolutely can, and in fact must, end it with a question mark. There are some cases where it is a little softer. For example:

Perhaps we can talk later.

This is kind of half way between a question and a statement. It is grammatically a declarative statement, so should not have a question mark, but it has a questioning subtext to it. You'd expect the response to be "Yes we can.", or "No I am busy." In fact, failure to answer would be pregnant. The failure to answer would be quite similar to the failure to answer the literal question you posed.

BTW, your tag was shall-will, however my answer would be the same irrespective of your use of either verb here. "Shall we talk later?" and "Will we talk later?" although different in meaning, are both still questions.