What is the companion that allows you to locate a file if you only know part of the name?

By companion, I guess you mean wildcard.

Let's say the file name is lostfile.txt.

The first wildcard is the *. If you remember the first part of a file was lost you could type lost*.txt. If you don't remember it was a txt file, you could type lost*.*.

Now for another wildcard, the ? If you were looking for a lostfile2011.txt and you couldn't remember which year it was, you could type lostfile20??.txt.

You could combine the two by typing lostfile20??.*.