Why Are There No / Missing Questions in My Lab?
In Diablo Highway, lab questions are broken into two categories, questions for the control samples and questions for collected evidence. The questions related to a piece of evidence are not available until that evidence has been found at the crime scene. If you are missing evidence you will also be missing lab questions.
In the case of the DNA and Shoe Impression labs there are no questions for the control samples, only for evidence. Therefore if no evidence has been found you will not see any questions at all in the lab.
If you try to submit a lab when you have not yet found all the evidence needed for it, you will be notified and your lab submission will be blocked. In order to submit the lab for grading you must find the remaining evidence and return to the lab to answer the related questions.