Filibustering is the process in that one party attempts to block sth proposed by another party. ??
Filibustering is the process in that one political party in a legislature attempts to block legislation proposed by another political party.

I think "in that" or "in which" is proper words in the sentence.

But I don't know exactly..

Question

Filibustering is the process in that one party attempts to block sth proposed by another party. ??
Filibustering is the process in that one political party in a legislature attempts to block legislation proposed by another political party.

I think "in that" or "in which" is proper words in the sentence.

But I don't know exactly..

Answer

"by which" would be the best choice here.

- the process by which something happens

Answer

The correct phrase is "in which."  The phrase "in that" means "because" and doesn't fit your sentence.