Is it possible to replicate the Thomas Henry X-4046 circuit using the PLL_Virtual component in Multisim?
That 4046 has nothing to do with Thomas H., he just used that chip in his circuit. No need calling it "Thomas Henry X-4046" just "4046 PLL" is sufficient.

Have a look at this datasheet page 11:



There you see that pin 11 is connected to the source of an NMOS. That circuit converts the input voltage from pin 9 (the VCO input) into a current which flows to P1.

So pin 11 is a current input, it wants you to sink a current from it to ground. That's what Q2 does in Thomas H.'s circuit.

Your PLL model very likely only accepts a voltage as input.

The circuit around Q1 and Q2 is for frequency modulation, you can achieve the same by just adding a voltage to the voltage you already apply to the PLL model's input.

How to exactly implement that depends on your circuit and goes too far to describe here.