Interested in Language
Is it correct to turn the sentence "He'll be her six husband" into a question" Which husband of hers in a row will he be?"
Any other alternatives?
"Invading armies have no rights." Noam Chomsky
This kind of question crops up quite regularly on this forum. Usually, people want to know something like how to ask what "number" president is currently in office. Barack Obama is the 44th President of the US. There is no natural way to ask for this ordinal number response. The unnatural/ungrammatical suggestion is usually something like "How manyeth president is Obama?"
As you have found with your question, there is no natural ordinal-based question which elicits the response "He'll be her sixth husband".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
***** NOT A TEACHER *****
I did some googling, so I believe that some (many?) native speakers (at least here in the United States) would find the following dialog(ue) acceptable.
Mona: How are you and Tony doing?
Betty: Oh, we have agreed to a divorce. We will continue to be good friends though.
Mona: Won't you be lonely?
Betty: Oh, no. I plan to marry Raul next year.
Mona: Congratulations! May I ask a question?
Betty: Of course.
Mona: Which/what number husband will Raul be?
Betty: My sixth.
(I noticed that with the word "husband," there were many more results with "what" than with "which.")