You can use a single Notezilla license on 2 Windows computers. This is if you purchase the "One time payment" plan. The "One time payment" license doesn't automatically sync sticky notes between computers and also doesn't give you access to your notes from your smartphone (Android/iPhone/iPad).
We do have Notezilla - Subscription plan.
With subscription plan, you can install Notezilla (Windows version) on any number of devices and PCs as long as all are syncing using the same sync account, plus all are used by same user.