We recently rolled out a survey to our users and had about a 19% response rate. I posted about it in the community a few weeks ago and provided screenshots of the questions that we asked our team members:
https://one.workfront.com/s/question/0D54X000073pyZUSAY/has-anyone-conducted-internal-surveys-to-gau...
I will say, one thing that I regret not doing for our particular use case is emphasizing that we wanted their feedback on the tool itself, not the processes that are built within it. We received some feedback/ratings that were very clear that the user was providing their responses based on the fact that they dislike the tasks within the workflows. Each department determines their own processes, we just build WF to accommodate what they ask for. So if someone has an issue with the tasks, they need to take it up with their department head, not us.