This card does not feature Instrument (Hi-Z) inputs.

To connect a guitar, use either a preamp with an Instrument input or a DI box with Hi-Z capability.
Depending on the output options of your preamp, you can connect it via Analog IN or ADAT IN.

Alternatively, connect the DI box directly to an Analog IN.

Yes, I forgot to mention that there are active and passive DI/boxes.
It might be that he might need an active one.

I am not using such boxes but there seem to be enough good active models available if needed,
but the better ones seem to have their price; therefore I am very lucky that the Instr inputs of the UFX III do the job so well.

To put only two examples from a quick research in this shop:
https://www.thomann.de/de/radial_engineering_jdi.htm
https://www.thomann.de/de/rupert_neve_designs_rndi.htm

The first is passive and I also doubt the second one has enough level for a pure line input. You really need to know the exact output level.
I think the best choice is a preamp with an instrument input.