This is a Trefoil Knot defined mathematically by:
x = sin(t)+2sin(2t)
y = cos(t)-2cos(2t)
z = -sin(3t)
for t between 0 and 2pi

This one was made by using Python to calculate 100'ish points in xyz-space and load them into Fusion 360 as an spline. Then add a tube to the spline path and export stl-file.

csv-file with xyz coordinates can be found in the files, so you can try it yourself. You find the spline csv import under add-ins.

Yes

The finer the better

Remove support.
Sand if needed.