The gain will be constituted by actual JFET gm, source and drain resistors and possible load impedance. JFET have a relative large type variation, indicated by the Idss and Vgs(off) range in the datasheet. Depending on the actual gm, the voltage gain of this circuit isn't necessarily larger than 1.
As a first point, you want to check the actual operation point by measuring the J201 source and drain voltages. Knowing this values, you can calculate actual gm and gain.
Simulating the circuit in Ltspice is a simple way to understand it's operation better.