Partner that i've been sexually active for the past few months just tested positive for mono, when should i get tested? i was ill with mono-like symptoms this past week but have been feeling much better with less symptoms for context?

It is a benign illness, there is no need to confirm if you have mild symptoms and you have recovered.

You can do it any time, but if you continue to feel well testing is optional. It is likely you were exposed and infected; you could even have been the source of your partner's infection. But almost everyone acquires EBV, the virus that causes mono, by their mid-twenties. OTOH, diagnosis would allow you to be on alert for complications, like enlarged spleen with risk of internal bleeding.