That's because you did not follow my example. You need to specify your clish commands in quotes, as it is made of more than one statement. Type:
clish -c 'show arp dynamic all' | grep 10.110.12.162
Without the quotation marks the clish command will fail and instead print the help page, where your grep does not find anything at all. E.g.
[Expert@MyFirewall]# clish -c show configuration
Usage-
clish [-d DebugLevel -i -l ExtLck -s -o OutFmt { -c Cmd | -f File }]
-c Cmd ;Single command to execute.
-d N ;Debug Level in which shell should operate.
-f File ;File to load configuration from.
-i ;Ignore cmd failure in batch and continue.
-l ExtLck ;Use the given lock-id.
-o OutFmt ;Output format (pretty, xml, structured).
-s ;Issue 'save' at the end.