In my JLPT workbook, I have the sentence:
I'm not sure what OB, OG訪問 means.
"OB" and "OG" mean "Old boy" and "Old girl" respectively. "Old boy/girl" means an alumnus of something, or a previous member -- usually in reference to a school or club.
So for this example, it says "By meeting with an OB/OG, they arrange an appointment...". Although I'm not sure if the OB/OG here is one from their school (who has already gone through 就職活動 themselves) or of the company they are applying to, though the former seems to make more sense.