Where one has a subject mastered, makes up suggestions to drink a measure of spirits (2,4,10)

'where one' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'a subject mastered makes up suggestions to drink a measure of spirits' is the wordplay.
I cannot quite see how this works, but
'a' could be 'one' and 'one' is found within the answer.
'suggestions' could be 'tips' (tip is a kind of suggestion) and 'tips' is present in the answer.
'measure' could be 'finger' (finger is a kind of measure) and 'finger' is present in the answer.
The remaining letters 'ats' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'has' is the link.

Can you help me to learn more?