What plants flowers zone6 koi pond morning sun would you recommend

You are in Zone 6a.

See if these sites help!

https://www.planetnatural.com/koi-garden/

https://koi-care.com/importance-aquatic-plants-koi-pond-choose/

I live in the same zone as you. I have 2 water lilies in pots that are placed in the deepest part (3 feet) . I leave them in all winter. How deep is your pond? Mine has a ledge that is only 12" deep around 3 sides. On those, I have papyrus, water iris, sweet potato vines, bog lilies and more. Those, I bring inside for the winter months. Just like other bulbs. I'm just putting mine back out this week. I pot all my plants, because the koi eat the roots and destroy them.

http://www.bonniesplants.com/zone_hardiness_and_light_require.html

Take a photo to a local nursery and ask for their advice. They only stock plants that thrive in your region.