How to find out which key is the Sysrq

My Ubuntu 18.04 -whole system- freezes regurlary. It is a Dell Latitude 3510. * I tried the Alt+PrintScreen (5mp)+r+e+i+s+u+b (2 mp delay between keystrokes) and the same with Alt+Home at the start. * Also tried this two while holding down the Alt constantly. * My sysrq is enabled, cat proc/sys/kernel/sysrq showed a value 176 - what ever that means. * The only way to shut it down is to take out the integrated battery from the inside of the laptop. Is there a way to find out which key "hides" my SysRq?