Need help with a formula field -- Trying to populate a new field based upon whether or not the original fields are blank or not.

Try this

List("\n",
IF(Trim([Question 1])<>"","Question 1 taken"),
IF(Trim([Question 2])<>"","Question 2 taken"),
IF(Trim([Question 3])<>"","Question 3 taken"))

The result would be a vertical list like 

Question 1 taken
Question 3 taken

If they answered questions 1 &3.

The report filter could use the contains as a filter like 

where [Questions Taken] Contains 1

Thanks for your help.  This is not quite working the way I had intended.  When I tried the above it is grouping in the filter as:

Question 1 Taken

Question 1 Taken
Question 2 Taken

Blank

What I really want is just:

Question 1 Taken

Question 2 Taken

If there are blanks they should be excluded.  When I refer to the filters they are the dynamic ones on the report, not within the report criteria.  I don't want it to be grouped into a new filter option if the user answers both questions.  The use case is tricky and perhaps it would be easier for me to send a screen shot and full use case?  Unless the above makes sense and is something simple I am missing. Thanks again.

If you want a Dynamic filter you will need to make three fields and have three dynamic filters, not one dynamic filter with three choices.

So just make a formula for [Question 1 Taken] with a result value of Yes or No.

Get that working then duplicate the field twice and adjust the formula for the other two questions.