Do diesel engines have knock sensors?

Probably not:

Knoking is the combustion of the fuel mixture before the actual ignition took place. This self-combustion is most commonly caused by high revving of the engine: the mixture becomes so hot due to rapid compression it ignites without a spark.

Diesel engines don't compress a air-fuel mixture, but only compress air. The fuel is injected when the piston is at top position (approximately), and ignites at that very moment; the compressed air is hot enough to cause ignition.

The timing of ignition in a diesel engine is therefore correct, also if you compress the air much more than with a petrol engine. This is in fact what is done, (compression ratio diesel is much higher than petrol, this fact makes this possible). This higher compression ratio gives a higher efficiency; as you'll probably know diesels are more fuel efficient.