Sorry if this has been asked and answered elsewhen/where, but I was unable to track anything down on this particular use of Exploit:
Say you’ve taken an Exploit Standard Action, and gained two Momentum which you intend to use on your attack next turn. In the interim, the target you’ve Exploited attacks you and you invoke your Riposte to make a counter-attack. Does the Exploit bonus (Piercing 2, etc.) affect the counter-attack, or only the Standard Action attack you’d be making on the next turn?