The easiest thing is to hold down alt + print screen (sysrq) and press c while still holding them
It does the same as
echo c > /proc/sysrq-trigger
A little explanation: the sysrq key is used to send low-level commands to the kernel itself, as a last resort to try to save the system. If you hold alt + print screen(sysrq) down and press another key next to them, it does the same as if you were to echo the key in that sysrq-trigger file. They call it trigger for a reason ;3
The 'c' tells the kernel to crash (cause a kernel panic)
However, you may want to see the content of 'proc/sys/kernel/sysrq'. If it is 178 or anything else, you should change it to 1. 0 is all disabled, 1 is all enabled, and anything larger than 1 is a bitmap for the specific things the kernel allows to do with sysrq.