Are sentences that have multiple "WH Question" words considered grammatical ?
For example, is the following sentence grammatical:
Tomorrow, where are we meeting at what time to do what ?
Yes, but you need some an and or two in there to join the three clauses/sub-questions into one:
Another valid example:
Both sentences are asking more than one thing, but it's possible to join them into a single question. But for clarity, it might make more sense to use more than one question.
Multiple "Wh" questions are definitely grammatical. However, your example has slight problems. Correcting them, it comes up with:
Yes, but usually only if the WH phrases are coordinated.
Hugo and Thursagen have both corrected your question by adding commas and "and"; but that changes the structure of question to create coordinated questions. So Thursagen's
is equivalent to
There are some simple cases where multiple WH's are allowed without coordination, such as
but to me these are informal. I can't come up with a clear rule about when this is acceptable.