Most everybody has done a good job responding.
I've done quite a bit of reading/reviewing on this while writing and publishing our CEN review course/manual.
The majority of 12-lead "core" ED nurse knowledge is to readily identify those major infarct/injury patterns and be able to anticipate particular interventions/treatments.
The main ones to know: Inferior, Septal, Anterior, Lateral ("I See All Leads"), and Posterior.
You should know which vessels affected: LAD, RCA, Circumflex.
And; be VERY familiar with your "routine" ACLS Lead II rhythms (Vfib, Vtach, Asystole, PEA, 1st/2nd/3rd Deg HB, Sbrady, Stach, SVT, PSVT etc)
Hope this helps....