"Grub up", you understand (3)
I believe the answer is:
dig
This could be a double definition.
'grub up you' is the first definition.
'dig' can be an answer for 'grub' (thesaurus). I'm not certain of the 'up you' bit.
'understand' is the second definition.
(digging is a kind of understanding)
Can you help me to learn more?
(Other definitions for dig that I've seen before include "critical remark" , "enquire more closely" , "Maybe break new ground" , "Understand" , "Sharp poke" .)