You'd run wireshark to capture packets from the swtich - If the switch has a default gw configured you should see his IP.
e.g. my switch has .151 and is looking for the default gw of .254
214 26.557654 ExtremeN_8b:d2:98 Broadcast ARP 60 Who has 172.25.25.254? Tell
172.25.25.151
But I still think the best way to access the switch is the console e.g. if the switch has no IP - right now we only assume there is one configured
Here the console port settings of the switch...
Configure the terminal to the following communication settings:
VT100 emulation, 19200 baud, no parity, 8 data bits, 1 stop bit, no
flow control, ASCII character set