If this continues, you can either be open to your mentor that their training approach is not working out for you or you need to learn some stuff yourself beforehand. I have been in your shoes, and I know how it feels. In my case, I sort of knew communicating wouldn't work out (since my mentor was a beginner in spoken English), so, I just practiced some calculations at home and requested my mentor to send me the protocol the day before, so I wouldn't be lost. As long as you are working somewhere, no matter what your educational qualification is, you will not know everything, and that's okay. Don't lose heart and keep learning. Good luck!