It's definitely not hollyhock. Unfortunately, it doesn't look ripe enough to contain viable seeds. Did your coworker see the plant? If there's any knowledge to compare, you may want to google Datura and see if that's a match. That's what it looks like to me. A pod with ripe seeds would be cripsy, brown, and starting to develop cracks/openings at the tip. Maybe your coworker can ask the plant's owner about obtaining a more ripe pod later. Someone with more experience could better advise you about growing the seeds. I've only had bought plants.

That's a datura seed pod, but it's not ripe yet. Wait until the stem is tan/brown and the pod begins to crack (it will take on a yellowish cast) before harvesting the seed pod. After the pod cracks, scoop out the (many!) seeds and let them dry on a shallow plate for a week or two. Then put in an paper envelope, medicine bottle, or such and store them in a cool, dry, dark place such as a drawer or closet shelf. If you store them in ziploc bags, make sure they are bone dry or they will mold or rot.

Datura is an annual, so wait until spring to sow the seed. I winter/spring sow mine. They will also self-sow. They are easy to germinate. Plant in the ground when small because they develop a tap root and don't like to be moved once they get any size to them. If you prefer to direct sow them, wait until the ground is consistently warm. When the heat comes, Datura really takes off. It has large, trumpet-shaped blooms (white or white-purple depending on the variety) that attract many pollinators. Datura blooms last only a day but keep coming for months, at least in my zone.

Barbara in Virginia, zone 7

Thanks, you guys! I will pass this info on. A friend told me it's a moonflower, which I just looked up and sure enough, that's in the datura family, which you both id'd it as. Very helpful.