Verbatim from Sametime support.
File location
The palette data and image files are stored on your local drive; the
location of the stored files varies by Sametime client type (Connect
or embedded) and version. The relevant subdirectory, which will be a
subdirectory of the main program directory, is
plugins\com.ibm.collaboration.realtime.palettes.
To identify the full path location for emoticons when using a Sametime Connect or Notes embedded client, do the following:
Open a chat window with yourself
Insert an emoticon, and click Send or press enter
Right-click the emoticon, then select "Copy Image Location"
Paste the location into a text editor, like Notepad. You now have the location for your client's palette files.