Has one understand one isn't given tick (4,6)
I believe the answer is:
gets across
'understand one isn't given tick' is the definition.
I can't judge whether this definition defines the answer.
'has one' is the wordplay.
'has' becomes 'gets' ('get' can be a synonym of 'have').
'one' becomes 'across' (I can't justify this - if you can you should give a lot more credence to this answer).
'gets'+'across'='GETS ACROSS'
Can you help me to learn more?
(Another definition for gets across that I've seen is " Manages to communicate".)