The Piper Cherokee 180D I am flying doesn’t have a published Vg in the POH.

[Pinecone]

It’s about 80 in ours when just me and instructor and utility weight.

Try it out. We worked with 85 too and found rate of descent to be worse than about 80. Still going to be a lot more difficult to nail a forced approach practice then typical Cessna.

Minimum sink speed is different from best glide speed.

Best glide is maximum forward distance for altitude. Min sink is the slowest rate of descent and will result in less horizontal distance.

Your instructor should know this.