The most common and most likely answer to this crossword clue is the 8 letter word RELATING
I've seen this crossword clue in The Daily Telegraph
R
E
L
A
T
I
N
G
Buddy explains!

The straight part
We know that "Telling" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case telling = relating.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 RELATING mean?
RELATING verb- To tell in a descriptive way.
- To bring into a relation, association, or connection (between one thing and another).
- To have a connection.
- To interact.
- To respond through reaction.
- (with to) To identify with; to understand.
- To bring back; to restore.
- The act of relating, or forming or identifying relationships; relation.