Hi

How can in blender made good thorns Ive noticed this model not hot have thorns,
https://grabcad.com/library/crown-of-thorns-obj-1 but render had them. So ive wanted made them at my own.

You can attempt to model spikes (or thorns) into the current geometry by beveling certain vertices. Similar techniques are demonstrated in this video:

You can also try using the Poke tool ALT + P on keyboard https://www.youtube.com/watch?v=0rXDVF_PijA . Using the poke tool to create spikes or thorns requires a base geometry which is relatively low poly and made from quad polygons to get a proper result. This may or may not be easily accomplished in the current model you have there.

Yet another alternative is to extrude geometry along a curve and then taper the shape. That technique will provide you with the greatest amount of control over the final shape of each thorn. Finally, even more simple would be to create a Cylinder, then taper the top by scaling down the vertices... this is probably the easiest method to accomplish. Of course, the problem in making the thorns from separate geometry is that you will then need to duplicate the shape and place the resulting thorns where you need them on the object you currently have.