What is the suffix for word crepitus?

The word "crepitus" doesn't have a suffix in the traditional sense. It's a Latin word meaning "crackling" or "rattling".

However, if we consider the ending "-us" as a suffix, then yes, "-us" is the suffix of "crepitus". But it's important to remember that "-us" is not a suffix that modifies the meaning of the word in the way that, for example, "-ing" or "-ed" do. It's simply the standard ending for masculine nouns in Latin.