if you are trying to see if the injector earths are pulsing,
that doesn`t tell you they are squirting fuel,
removing them from engine and hooking up to the fuel rail would do 2 tests at same time, but yes you can probe the wire on each injector to check if its pulsing, by slipping a probe with a test light, into the back of the plug on each injector plug
, I believe the live is constant to each injector with ignition on, and the earth wire is pulsed by the ecu