I removed my old medicine cabanet that had two lights attached to it from my bathroom wall. I found two 14/2 wires coming into the junction box that these lights were wired to. I am installing a new light fixture only to replace these old one. Which one of these two 14/2 wires do I connect my new light fixture to?

Just connect the new one exactly the same way as the old one was wired.

I will assume you have a connected wire set from one light to the other. Disconnect both sets and find the matched pair. With the switch off, temporarily connect the new light to one pair and turn on the switch. If it lights that is the pair. If not, it's the other pair. Or use a VOM to check the voltage.

I believe you are looking at a "Supply Line cable" and a "Switch Loop cable."

Of course that is guessing that you have a light switch controlling these lights,

If this is true, you must first determine which cable goes to the switch and which cable is bringing the supply voltage to the junction box.

Once you know which cable has the black & white from the feed, you connect the black from the feed to the white to the switch. NOTE: please mark the white wire to the switch with either a black sharpie or wrap it with black electrical tape at both the junction box end and the switch end.

Next, connect the black return wire from the switch to the black lead for the light. Finally, connect the white from the supply cable to the white from the light. Also connect all bare or green wires together and to the junction box if it is a metal box.