Knowing where to go — perhaps, try it on a pet dog at first! (5-7)
I believe the answer is:
potty-trained
'knowing where to go' is the definition.
I can't tell whether this definition defines the answer.
'perhaps try it on a pet dog at first' is the wordplay.
'perhaps' indicates anagramming the letters.
'at first' suggests taking the first letters.
The first letter of 'dog' is 'd'.
'try'+'it'+'on'+'a'+'pet'='tryitonapet'
'tryitonapet' is an anagram of 'pottytraine'.
'pottytraine'+'d'='POTTY-TRAINED'
Can you help me to learn more?
(Other definitions for potty-trained that I've seen before include "(Of small children) no longer dependent on nappies" , "Weaned off nappies" .)