i assume you're talking about rental tech. For that you dont need to know much about skis, because the shop will probably have them organized so you can figure it out pretty easily.
If you're gonna be a retail tech, the easiest thing that i have found, is tell them you are good at remembering things. To proove this, once you start working, grab the brochures of the companies you are selling. Most companies keep the same construction for all their models, so just review that stuff.
for example, most K2 Skis are a wood core with a triaxel fiberglass wrapping and a 360 cap construction (except new public enemy and i think Seth pistol are sidewall, BUT this is identifiable by looking at the ski).
Line skis uses the same triaxel fiberglass wrapping, and they use a pine/poplar core and 360 seamless cap on all their skis.
I especially like the Dynastar, which incorporates cap construction on the tip and tails, and a straight sidewall running the span of the contact points (the points of contact when the skis are put together base to base).
Most of the stuff you can tell by looking at the ski, just study the flex. Companies usually make it easy to know by marking flex and sidecuts of different skis by numbers, for example the old K2 Merlin had 1-5, higher number, stiffer straighter ski.
hope this helps ya out!
'I step into another level when i smoke that herb, style is everything, gotta be mooth.' -Tanner Hall