In Instiki 11.0 your system password is stored with the rest of your data in the the file production.db.sqlite3. It is stored in the system table in the database and is not encrypted.
You will need something that can view the sqlite3 database file, such as SQLite Database Browser and then use that to open the file. Using that particular program, after you open production.db.sqlite3 with it, select the “Browse Data” tab, and the from the drop down menu choose the “system” table. In my Instiki installation the only information stored here is my system password.