I am wondering what this is called, and what the best way would be to get this cutting started growing. Cut, let callus, put in ground or water ? Thank you for any help on this !!

It looks like an Euphorbia, maybe Euphorbia paralias (syn:Euphorbia maritime)?
Was it growing by the coast and in what location?
https://www.google.be/search?q...

It was growing very well outdoors all year in Minnesota (zone 4a). Does this sound like it could be right ?

Or maybe Donkey Tail spurge?

Yes! I think that is it ! Thank you Do you happen to know what the best method of propagation would be for what I have? I have read about few different methods, but am unsure what would be best. Perhaps this is a question to be asked in another forum?

If it's E. myrsinites, and you have one, you won't need to worry about propagating it - it will take care of that all by itself. That being said, when I decided to move it out of one area where it was taking over, I just pulled it out by the roots, and stuck it in the ground elsewhere. They all thrived and multiplied very quickly. Beware the milky sap if you have skin sensitivity to latex. I like to use it to fill in areas where the soil is poor and it gets no watering. It did try to take over my rock garden and I had to put a stop to that!

I don't have the plant, but am hoping to get this cutting to root. I have gotten a response in another thread and am excited to get this to grow! thank you!!!