Yes, Nokia 7 Plus does have the headphone jack, which is located on the top panel of the phone.
Yes, Nokia 7 Plus does have the OTG support.
Yes, you can record 4K videos with Nokia 7 Plus at 30fps.
Yes, Nokia 7 Plus in-the-box accessories include a pair of an earphone as well.
Great battery life, immersive display, solid design, and software at its purest, that's the Nokia 7 Plus for you.