I don't think Xizor knew the ways of the Force, But if he wanted to replace Darth Vader as Palpatine's right hand man and succeeded in having Luke killed and Darth Vader gets killed for failing his Master, Would Emperor Palpatine train Prince Xizor the ways of the force and make him his new apprentice?
Seeing how Xizor wasn't Force-sensitive, he would never be a Sith Lord. Very little reason, if any, to learn about the Dark Side if he can't even use the Force to begin with.
Indeed. The only thing he might have learned to do, but probably already had mastered, was the use of his natural Faleen influencing abilities, which were pheremone based were they not?
Third most powerful man in the galaxy indeed. Xizor was a little kid playing in the big kid's sandbox, and he didn't realize that just because some people weren't flashy didn't mean that they couldn't squash him like ants. Since Pestage was mentioned, even the likes of him counted for much more on the galactic stage.
That somehow didn't stop his from being the Third most POWERFUL figure in the Empire. Speciest or not, the Empire tolerated those aliens who were useful. To a certain extant at least.