I am looking for a way to monitor the raw USB HID events generated by devices such as keyboards, mice and other similar devices. There used to a IOUSBFamily kext with logging enabled that could be installed that would do this, but Apple hasn't updated it since OSX 10.9, so it doesn't seem to work anymore.
Look at Little Flocker (monitors file access) and Micro Snitch. I have both, as well as Little Snitch, which monitors network traffic. It can be quite confusing when all these messages pop up, sometimes ten in several seconds. Best is to try one, see how it works, get a feeling about it, then install another, etc.