From 2007......if you are a 121/135 person from another carrier they will expect a 121 level of knowledge of your a/c. You may not have to draw out the schematic but you better be able to explain the system using boxes / lines / circles etc. You don't need to be an artist but you need to have a working knowledge of the systems on your plane. One of the ground instructors summed it up thusly...."You don't have to build of fix the Da*n thing just know what to do so it won't kill you!"
If you are a 91 guy they will expect you to be able to do the same for the most complex a/c you are teaching or flying. I was an instructor, in my tech I had to draw out how an electrical circuit worked in any airplane and then draw the fuel system of my twin trainer. I also had to explain turbine theory in more detail than suck squeeze bang blow. Don't forget about the Jepps either....Have fun and be yourself!