According to Mike, current monitor for subckt is not implemented in Qspice yet.
Plotting pin currents of custom created symbols - QSPICE - Qorvo Tech Forum
A MOSFET modeled by a .subckt (Symbol type : X), I normally use a 0V voltage source for current monitoring, just remember that current direction (+ve current) is from +ve to -ve terminal within voltage source. In default, if you hover and probe current of voltage source, it will auto assign a negative sign in plot, as in most cases, you would like to monitoring current coming out from voltage source. The fast trick is to hold SHIFT key to probe current in 0V voltage source, as it can give +ve current in plot.
