Bokeh occurs when highlights are outside the DOF (Depth Of Field) range of whichever lens you are using. It can occur from highlight in front of the DOF and behind it. In this case, they are all behind.
The shape of these out-of-focus highlights is determined by the number of blades in the aperture diaphragm. The more blades, the more round the bokeh typically appears.
Typically this kind of bokeh is achieved with a large-aperture lens - say F1.4-F2.8 range, but it can be achieved with F5.6 too, provided that the highlights in the background further away from the subject you are focusing on.
Some lenses produce "nervous" bokeh. The highlights are out of focus, but appear with so much contrast that they actually draw attention away from the main subject, so not every lens is equally suitable for these kinds of shots.
Good places to experiment with this is in the evening in a city - the many different lights you often have there from traffic, cross-walks, store fronts, lit advertising etc. etc. produce a vast landscape of opportunity.