The most common and most likely answer to this crossword clue is the 6 letter word REMIND
I've seen this crossword clue in The Guardian
R
E
M
I
N
D
Buddy explains!
The straight part
We know that "Make one think again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case make one think again = remind.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does REMIND mean?
REMIND verb- To cause one to experience a memory (of someone or something); to bring to the notice or consideration (of a person).