The answer to each clue below is a two-word phrase, and each phrase begins with the same first word. That  word is a homophone for one that is usually used in the phrase.

1. Be uncertain
2. Shake in one's boots
3. Cry over spilled milk
4. Be the butt of the joke
5. Be proficient at certain gambling game (slangily)

Answer:

1. Know doubt  (No doubt)
2. Know fear
3. Know regrets
4. Know kidding
5. Know dice

Credit:
Harvey Estes
JUST SAY "KNOW"