How do I connect an old iMac to MacBook pro?

My friend asked me to find something on her old iMac. I thought I would connect the iMac which is very old., to my MacBook Pro, but then realized I had no idea how to do that.

I do not know which OS is on the iMac, but I do know that the OS cannot be updated. I think the iMac is probably at least 10 years old. This is what the post on the iMac look like.

I do have a USB-C Digital AV Multiport Adapter.

If I have not provided enough information please let me know. Thanks.