Take another look at the sentence:
Watching the second hand sweep the clock, Dr. Grayson's boring lecture on
the French Revolution seemed as if it would never end.
Watching the second hand sweep the clock, a participle phrase, comes right before lecture, an illogical target. [Dr. Grayson's, a possessive noun, functions as an adjective describing lecture.] Students, not the lecture, watch the clock! Before you continue, review the rules for misplaced and dangling modifiers.
Go back to the sentence to try again.