The most common and most likely answer to this crossword clue is the 10 letter word QUIZMASTER
I've seen this crossword clue in The Daily Telegraph
Q
U
I
Z
M
A
S
T
E
R
More clues leading to the result QUIZMASTER
Buddy explains!
The straight part
We know that "Host who knows all the answers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case host who knows all the answers = quizmaster.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 QUIZMASTER mean?
QUIZMASTER noun- A person who poses questions to contestants on a quiz show.