A good research question is, obviously, answerable by research, or at least it seems answerable at first. It describes a theory that will be researched in a way that other researchers can understand and attempt to repeat.
The theory on which the question is based must also be falsifiable and parsimonious, testable, be able to predict future tests of it, repeatable, and general enough to apply to more than one situation (Johnson et al., 2014).
Johnson, R.B. & Christensen, L. (2014). Introduction to educational research. In Educational research: quantitative, qualitative, and mixed approaches (p.19). Thousand Oaks, CA: Sage.