How do I get Spam Assassin to work on the domain level in plesk? I have activated it at the server level and put a check mark in USAGE POLICY LEVEL > PERSONAL SETTINGS..

But then when I go to the domain mail settings it shows that SPAM ASSASIN is disabled.

Some things to check...

From the cp go to Server > Services Management to verify that SpamAssassin is running

Then go to the domain in question and into the Mail icon. Choose one of the email addresses. Choose the Mailbox icon. Make sure Enable spam filtering is checked.

If all of those are done the SpamAssassin icon should be clickable.