"When in doubt, use brute force."
The tooltip text will be saved somewhere, with a good chance of that being in the executable that displays it.
You can extract strings from the executable in question, e.g. with a utility like Strings (Microsoft) and search the output for a word or two from the displayed tooltip.
Usage: strings.exe [-a] [-b bytes] [-n
length] [-o] [-q] [-s] [-u]
Strings takes wild-card expressions
for file names, and additional command
line parameters are defined as
-s Recurse subdirectories.
-o Print offset in file string is located.
-a Scan for ASCII only.
-u Scan for UNICODE only.
-b bytes Bytes of file to scan.
-n X Strings must be a minimum of X characters in length.
To search one or more files for the
presence of a particular string using
strings use a command like this:
strings * | findstr /i TextToSearchFor