How to determine the degree of evenness of the surface?

Question

Summary

Let's say we're making a puttying robot.
Given: there is a relatively flat wall on which there can be all sorts of irregularities such as holes from a perforator, joints of gypsum boards and other pieces of plaster that have fallen off. Is it possible to "budget" to find them? With using what? CV, lidars, something else?
Thank you!