What is the value of resistors R2 and R5 shown on the schematic?

This module is designed to output 4-20mA current via I2C commands and is not intended for current measurement.
For your needs, we recommend using an I2C digital wattmeter. However, since the current you are measuring is very small, we recommend that you calibrate it according to the wiki before measuring.
https://www.dfrobot.com/pro...

Hard to say what the accuracy will be. Noise will be the limiting factor in this case, as the conversion on this unit is analog, and therefore has effectively infinite resolution. Adding up the noise of the op-amp, the temp coefficient of the opamp, the current ripple picked up through the wiring and then the SNR+D in the ADC itself, I'd find it highly unlikely you're going to get anywhere near 24 bits of accuracy unless you trust in your software filtering capabilities.

On that note, your ADC is most likely a Sigma-delta architecture (all the "20+ bit resolution" adcs out there are usually sig-delt), which means the samples taken aren't independent like a SAR, so any kind of statistics-based software filtering (which is pretty much all software filtering) is actually going to be effectively indeterminate. I would argue that makes it basically meaningless.

That's all to say you almost certainly won't get 24 bits (which would = .002% F.S.), however I would venture it's safe to guess you could get 18 bits out of it, maybe 19, so .1% - .06% FS resolution.

Not affiliated with D.F. Robot but that's just my 2 cents working on sensors and metrology for a few years.

Sorry for late. The screen off the shelf, but we have smple at the Wiki, you can refence.
https://www.dfrobot.com/wik...