How do Panglacial Wurm and Imoti interact?
No, you won't know what it cascades into.
Cascade is a triggered ability. This means that the ability triggers when you cast the Wurm, and then goes onto the stack once players receive priority. This only happens once you're done resolving whatever spell or ability let you search in the first place. At the end of the search, you are almost certainly instructed to shuffle your library (I don't know any searching effects that doesn't make you shuffle your library afterwards, but I don't know that none exist).
So here is the order of events:

You search your library, cast the Wurm, the cascade triggers
You finish your search, and shuffle your library as instructed
The cascade is put on the stack
Players have opportunities to cast instants and activate abilities
The cascade resolves and you exile cards from the top of your library

So the search that let you play the Wurm does not let you know what it cascades into. You would have to do something like a scry in step 4 above in order to know that. But by then you have already decided to cast the Wurm.