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> Furthermore, an amplifier symbol called "gm" is labeled as transconductor. What does it do? Transconductors are voltage-controlled current sources, but what are they doing here?

The diagram looks like a voltage output power supply.  I'll make a working assumption that it's voltage output power supply.  

[Access to the manual might shed some light on this.  Please post a link to the manual.]

> In the schematic, there is one resistor between sense and force line of each channel which I can't explain why it is there and what purpose it serves.

The resistor in question is R5 in the diagram.  Its value isn't given, I'll make a working assumption that the resistance is sufficiently large.

Its purpose is to tie weakly the Sense feedback input to the Force output when Sense terminal is disconnected.  That allows the output to maintain a sane value if the Sense input gets disconnected.  Otherwise the output could go crazy without any feedback connection, and potentially damage the DUT.  It also allows to omit the sense input intentionally at the expense of a larger output error.

![diagram with a few annotations](https://electrical.codidact.com/uploads/8f97tyas3lwe4u761cyztwevqbex)

When the sense terminal is connected externally, it's a low impedance connection, it overpowers the R5, and the current through R5 is negligible.