There is not much requirement for CAS in the fight against BH - let alone CAS of the complexity and power of A10 - because the BH very rarely stand and fight, and they have almost no assets or infrastructure. In any case, there is no way that the NAF (or CAF) could possibly operate such a complex aircraft. The US recently refused to sell them Cobra attack helicopters ostensibly for that reason (but also partly because of unease at the endemic corruption in the Nigerian military).
The NAF needs first more ISR assets (they only have a King Air and a DA42M) - but as ever the procurement will be determined by how much backhander the supplier will pay so they will probably end up with an overcomplicated, over-priced unreliable Israeli system since US and European suppliers cannot pay the required bribes.
In any case, the solutions for their problems with BH are institutional rather than military. Nigeria will lose the fight unless they sort out their staggering corruption problems whereby every person in public service from top to bottom is only interested in how much money they can make from their position. Even frontline soldiers sell their ammunition to BH...