ses-twee kwee vee
Here's a breakdown:
* Cestui: Pronounced "ses-twee" (like "sway" with a "t" at the end)
* Que: Pronounced "kwee" (like "knee" with a "w")
* Vie: Pronounced "vee" (like "see" but with a "v")
It's a French phrase, and although it's a legal term, it's often pronounced with a bit of an English accent.