There is an Euler circle on the octahedron's edges-net that takes a turn at every vertex. Let the two parts of the path that go through each vertex wind around each other, and you get this nicely symmetrical knot.
This knot is available in several versions, differing in the cross section of the rope:
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Circle
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Square
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Twisted square
- Rope (that's this one)
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Rope with fine detail
Be warned that depending on material, size, wire thickness, detail, complexity of the knot and the mood of the guys who do the manual printability checks, Shapeways may refuse to print it. I obviously did not test this for all of my over 300 knot models. You can tell whether a knot has been printed successfully before in the chosen size and material by looking whether it says "first to try" under the material selection box.