Selecting a Thesis - Are there lists of interesting or open questions?
You have two questions here. Addressing the broader one, of how to pick a thesis topic when none is jumping out, Umberto Eco's How to Write a Thesis is a surprisingly practical book. It takes as the premise that you have only six months left to write a thesis (Italian roughly masters-level thesis), with limited scholarly resources at your disposal. It's fairly short and encourages you to work with whatever you have. It does not assume you have much oversight available.

The answers to another question on finding (masters) thesis topics point to conversations with faculty.

The existence of a dissertation database has been addressed in previous questions (e.g. Worldwide Dissertation Database? or French, German, Italian ones?). That thread doesn't list Proquest, which indexes dissertations from many universities. (It's interesting to see the most-accessed Proquest dissertations.)