The original sentence:
Whatever it is, is what he is trying to find.
Can we replace whatever with no matter like this sentence below?
No matter what it is, is what he is trying to find.
By the way, I made this sentence up and I also expect you to correct my sentence if there's any mistake or to suggest another natural sentence. Thanks.
Best Answer
As @Richard Winters pointed out, it's a matter of context whether it works or not.
In your example, the "is, is" is a bit unusual. While your substitution doesn't work in your example, a small change makes it ok.
I changed the tense, because at the time some item is specified, the "finding" action would be in the past.