Like many other compact electric vehicles, the Kia e-Niro does not come with a spare tire.
Instead, Kia uses the spare tire well for a formed styrofoam insert with space for charging cables and perhaps a tire wrench and jack.
There is a discussion on the Niro EV Forum about how to install a spare tire. It appears that the retaining bolt for a spare tire exists, so installing a spare would be as simple as getting a spare tire from Kia and bolting it down.
Image Source: Alex on Autos Review