Re: help me to identify coating type and removal technique
A coating material can't be identified for sure from a photo, but it looks like silicone rubber (dry and elastic). It could be also epoxy molding (hard) or less likely silicone gel (soft and sticky). Silicone would be best removed mechanically (cut with a knife and peeled in pieces).
Any solvent that might be used to soften silicone rubber will most likely affect component packages and PCB, thus I wont suggest it.