It's the 1" rubber cap, edge of front door that allows access to the screw that holds the outside door handle on. Looks like a 1" metal hole plug from Home Depot will do the job. Or a short rubber stopper.
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was: 2005 2wd V8 Limited, one owner (me), 155K miles
now: 2019 Kia Sorento SXL V6
Sometimes the part is too small to part out separately. So in order to get the part you have to buy the whole assembly. They may not show a part in that detail if they don't sell it separately.