The only real way to check is to see what the SWR reading is. For that, you need the whole thing set up and a SWR meter put into the coaxial line between the antenna and the CB radio. You should aim for a SWR of 1 to 1.4 The only thing I can think of that you could check with the antenna 'unhooked', is to get an electrical multimeter with a 'circuit' function (to check the continuity of circuits). The main antenna should complete a circuit to the centre pin of the jack, and the ground plate (or fixing bracket) should complete a circuit to the outer ring of the jack. If either of these don't work, there is either a problem with the antenna or a break in the cable, but probably the latter as there is naff all to go wrong with an antenna.