You want to say a verb can or cannot get all the way to its outcome — not whether you will, but whether it can be done.
序 · The move
1Fix the verb and the result it aims at (看 + 懂, 看 + 完).Is the second word a real outcome of the first, not a separate verb?
2Decide reach or shortfall, and wedge the matching char between them: 得 for can, 不 for cannot.得 = it lands; 不 = it drops short — am I not running these backwards?
3Read it straight through: V得R or V不R, no 了 on the result.Did I leave off 不能/可以 — the wedge alone carries the possibility?
例 · Examples
1他看look at, read得reaches the result (can)懂understand (the result)中文菜單。我今天看不falls short of the result (cannot)完finish (the result)這本書。
He can read the Chinese menu. I can't finish this book today.
Same 得, opposite job and stress. Potential 得 is light and infixed before a result (看得懂, can); degree 得 follows the verb and introduces how it turned out (寫得好, written well).
Same grammar, two names. 可能補語 is the structural term for it; V得/不…（表可能） is the surface form a learner looks up.
✗ 我不能看完這本書 → ✓ 我看不完這本書 (let the wedged 不 carry the impossibility, not 不能)
✗ 看得懂了中文 → ✓ 看得懂中文 (no 了 on a potential — it states capability, not a finished event)
✗ 他看不懂得菜單 → ✓ 他看不懂菜單 (one wedge only; 不 already negates, drop the 得)
English packs can/can't into a modal before the verb (can read, can't finish), so learners reach for 能/不能 and skip the V得/不R seam that native usage prefers for reaching a result.