Student or Learner
I want to convey this idea:
They hadnít asked all the questions that they wanted to ask.
Is my sentence suitable?
They still had questions wanted to ask.
Why in the second sentence do you drop out "that they"? It should read:
"They still had questions that they wanted to ask."
In any case, the second sentence (as corrected) has a slightly different meaning since it is in the past and not the past perfect. Generally, though, they are almost the same and the point you are making will be clear; most people wouldn't detect much difference.