Is there a library of sample survey questions somewhere on the platform?

While Gallups Q12 survey may be proprietary, the concepts they use to formulate many of their 12 questions are not proprietary to Gallup. Here is a good primer to their engagement survey: https://www.gallup.com/access/323333/q12-employee-engagement-survey.aspx
We have utilized a qualtrics survey to annually track employee engagement at our work.