I would like to hear some ideas that can explain Greek *σκέπτομαι, σκοπός "watcher, look-out, spy, mark, goal"
from Proto-Indo-European *skep-ye-, from a metathesis of *speḱ-.
Cognate to Latin speciō (“I see”).
... especially the methatesis.
German schauen "to watch", En. "to show" are PGmc *skawwōną (“to look, see”), IE *(s)kewh₁-(“to heed, look, feel, take note of”). *(s)kewh₁- could conceivably relate to *h2ew- (Def. 2 "to perceive"). Could these have, for example, influenced the metathesis?