Turn debugging and select dhcp IP packets to debug.
no debug all terminal monitor conf t logging monitor debugging logging on exit debug ip dhcp server packet
Confirm that debugging is on using show debug; although, it is likely you will already be seeing dhcp packets if your network is moderately busy.
show debug # DHCP server packet debugging is on.
Observe DHCP packets... then turn off debugging. Note that show debug will return an empty line if all debugging is off.
no debug all terminal no monitor conf t no logging monitor exit show debug