Slope stability is one of the most cross-cutting topics on the PE Geotech —it appears in three NCEES sections: Earth Structures, Problematic Soil/Rock (as rock slopes), and Earthquake Engineering (pseudo-static).
One detail that trips people up: a water table at the surface with seepage parallel to the slope roughly halves your factor of safety. A 20° sand slope with φ'=32° drops from F=1.72 (dry) to F≈0.86 (saturated). Same slope, same friction — just water.
And here's the navigation trap: Bishop's Simplified formula isn't in the PE Reference Handbook. It's only in USACE EM 1110-2-1902. Both references are on-screen during the exam, but if you haven't practiced jumping between them, you'll burn 5 minutes hunting for the equation.
Full breakdown of the 5 slope stability problem types: https://pewise.com/blog/pe-geotech-slope-stability-exam-problems