(Not a teacher)
Perhaps this is going further than you wanted to, but in linguistics, 'question' is an illocutionary type; it's grammatical counterpart is 'interrogative'.
Often, people use these terms interchangeably, but they should be distinguished from each other.
Grammatically, "Would you mind talking more quietly?" is an interrogative sentence. However, it's illocutionary force (the speakers intention) could be as a statement, or perhaps a command, not a question.
For this reason, I would say that the question mark should be ommited if the illocutionary force is as something other than a question.
Similarly, if you make a statement (grammatical structure), but you mean a question (illocutionary force) then a question mark should be added in writing. So:
'You are going.' This is a statement, grammatically. However, it's illocutionary force can either be a command, or a question. This would be indicated by intonation and tone of voice. In writing, it would be indicated by the addition of an exclamation mark for a command, and a question mark for a question.
So, to clarify my point - if you say a statement (grammatically) and what you mean is a question (intention), then use a question mark. If you say a question (grammatically) and what you mean is a statement (intention), then don't use a question mark.
However, your example of 'how you join' is only a statement. Grammatically, 'wh-' questions (of which, 'how' is one) require an auxiliary to be added. Also, 'wh-' questions are very rarely used as statements because of this auxiliary.
