There are TWO sets of windings in a coil. (It's a step-up transformer, in reality.)
The "primary" side gets fed something around 12V (maybe less on some systems in certain cars, but at least 8V in all cases). The "secondary" side will generate between 40 and 60 THOUSAND volts. The problem is that the secondary voltage is a pulse of very short duration, NOT a steady level. Thus, capturing this on a meter is impossible.
Measuring the impedance of the coil is the only way to do a home-brew diagnosis of the coil's performance. The primary side is measures across the two small terminals on the coil. The secondary side is measured between the contact in the center of the coil, and the metal outer jacket of the coil, which is ground.
Coils can fail two ways:
1. by becoming open (no connection), and having infinite impedance. (OL)
2. by shorting internally, and having lowered impedance.
Replacement coils can be had for $20 or so at most parts shops, if the impedance measures bad.
HINT: BE sure to DISCONNECT all wires to the coil when measuring impedance, so as to not have other items that are connected thru the wiring influence the readings you get.