What is collective noun of wad?

There isn't a specific, widely-accepted collective noun for a "wad" of something.

The word "wad" is usually used for a clump or mass of something, and the specific collective noun would depend on what that something is:

* Wad of cash: You could use "stack" or "bundle" depending on how the cash is organized.

* Wad of paper: You might call it a "pile" or "stack".

* Wad of cotton: This might be a "ball" or a "lump".

So, there's no single collective noun for "wad," but the best choice depends on the context and what the wad is made of.