A couple of comments from the "take it for what's it worth" department ...
A good quality trickle charger will come with two sets of connector cables; one set will have alligator clamps like you'd see on jumper cables and a second set will have eyelets. I prefer to use the eyelets and leave the cable in place. This will give a better connection and I only need to use the quick connect plug for the charger. The eyelets are designed to mount to the nut and bolt on the battery cable terminal clamp as so:
On a negative grounded vehicle like the I Pace, you'll always attach the red positive terminal directly to the red terminal clamp on the battery or to a post inline with the battery cable specifically for this purpose (my wife's Range Rover has a special positive terminal for this purpose, but I don't see one for the I Pace). As for the black negative cable, you only attach that directly to the battery when the car is not equipped with a Battery Monitoring System (BMS), which the I Pace has, or when the battery has been removed from the car.
The negative earth "blade" described in lobster's post is designed for alligator clips, but that won't work for the eyelet unless there is a bolt attached to the blade which isn't visible in the photo. That means you'll need to find a bolt attached to the chassis preferably with bare metal exposed. The only candidate that I see in the photo is the bolt on the clamp that secures the battery to the vehicle, but I'd much rather find something more isolated unless JLR has specifically indicated this bolt can be used for grounding purposes. You may be able to follow the black negative wire from the battery and find where it is attached to ground.
It's not a big deal to drill a small hole in the sheet metal and then use a self tapping screw to create a ground point, but I'd rather look for a dedicated post first. I'll poke around the car this weekend if no one reports on a solution first. On an ICE vehicle, it's really easy to find mounting points for a negative earth terminal since the engine block is a great source for this. It may require a little detective work on a BEV.