How to get the current value of /alertson in Skype?
Yes, it is possible.
If you Right Click on the group chat's "tab", then click Notification Settings... it shows you your current alert keywords, allows you to change them, and adjust some other features.
Additionally, your user information and messages are stored in %appdata%\skype\[your username] on Windows and in ~/Library/Application\ Support/Skype/[your username] on OS X in a file called main.db. It's an SQLite database, so you could potentially programmatically retrieve or change the values if you wanted.