These work as regular runtime parameters, and you're probably better off putting them in the multichain.conf file so you don't have to set them each time. Inside that file you would use the following form:
blocknotify=/path/to/script %s
walletnofify=/path/to/script %s
If you want to use them on the command line, use the form -blocknotify=/path/to/script
Please note you cannot put the shell command directly in the parameter value - it needs to be a path to a file that can be executed.