There will be times when you momentarily forget the meaning of a character or word entry that you previously marked as Known. Instead of resetting the entry to Unknown, you will probably just want to take a peek at the entry definition or pronunciation.
Peeking at a character: In the Reader with the character selected, just press the spacebar. The character entry will appear in the Character Dictionary window.
Peeking at a word: Once you have marked a word as Known, there will be no indication in the Reader that the characters comprising the word actually constitute a word. You can press shift-spacebar (with a character selected in the Reader) to see if the character really is part of a word. If it is, the word entry will appear in the Word Dictionary window. If it isn’t, the Word Dictionary window will remain blank.