High cpu load in cpanel is a real headache for administrators. It can be due to no memory/no swap memory, high cpu usage etc. However simple way to track it to look at the processes going on or you can check WHM > Daily Process Logs to see if any user has high CPU, memory or MySQL usage for that specific day.
Other method involves using the command sar which is system activity report. It will tell you if your system had issue time wise though for digging deep we would need more information.
Use the top command in linux and press m to see if memory/swap memory is not full.
A graceful reboot is the last option just to see if things go around.