Your work context may provide you with frequent opportunities to do that.

For instance, if you are a programmer, you can make predictions about how long a given task is going to take, or alternately how many tasks you can take on in a given period.

If you train or teach people, you can predict what they will have understood at the end of a given session, and test those predictions by asking questions at the end of the session.

More generally, predictions of the form "I will achieve objective X by time T" are a useful class, as you normally have quite a lot of the relevant information, which ought to narrow your confidence bounds.

ETA: keeping appointments is another similar class. If you're never late, you're probably underconfident. (See Umeshisms.) You should have a general degree of confidence in your timeliness, e.g. "I will seek to show up on time 80% of the time." You may adjust that depending on criticality in given contexts, e.g. "...except that I hate to disappoint employers, so I'll show up to work on time 95% of the time".