Since I don't know the thickness of your coating and whether it is easy to be corroded, I suggest that you can directly use EBSD to have a look at it first. If you can't observe it, you can choose to etch it with a certain concentration of acid
Xinhui Geng brings up a great point about the coating thickness. The last thing you want is to completely remove the coating and obtain erroneous data. A comprehensive compilation of etchants and overall polishing techniques can be found in George Vander Voort's book "Metallography: Principles and Practice".
In addition to the answers provided, you can look at ion milling either by dual beam FIB or by other preparation techniques.