The most common and most likely answer to this crossword clue is the 10 letter word FORWARDING
I've seen this crossword clue in The Guardian
F
O
R
W
A
R
D
I
N
G
Buddy explains!

The straight part
We know that "Passing on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case passing on = forwarding.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 FORWARDING mean?
FORWARDING verb- To advance, promote.
- To send (a letter, email etc.) to a third party.
- To assemble (a book) by sewing sections, attaching cover boards, and so on.
- The act by which something is forwarded.