Given you have a 14 pin package it could be almost anything from a op-amp(s) to 74XX series logic.
Start with a continuity tester and see if there are any pins that are obviously shorted together. If so that would be a big hint that they maybe power rails. Also look for common pinouts (Vcc, Vss on corners pins 7,14 etc.). THen use a diode checker and to determine the connectivity of these pins, where to you see opens and shorts, Vforward etc. You will start to see which pins are wired and likely which are +'ve rails and ground -'ve rails. Do keep in mind that there will be ESD protection diodes you will see. If there are no diodes at all then there is a chance that that pin might be a Analog input.
Next set your power supply current limit to very low and power up the device via the pins that you thing are the rails. Be aware that you can power up a device through an input pin through the ESD structures, but that is noticeable because outputs will have a output voltage that is one diode drop below rails on them. Increase current limit and test probe and slowly work your way into understanding the chip, eliminating possibilities as you go. IS it an op-amp or logic? An open loop op-amp will act somewhat "digital" but probably won't go to the rails.
The permutations and combinations of possibilities and techniques rapidly expand from this point forward.