Which OSI layer you looking for?
Mac Layer:
MAC broadcast is ff:ff:ff:ff:ff:ff so the filter would be
"eth.addr!=ff:ff:ff:ff:ff:ff" (if you have wireshark >3.6) or
"!(eth.addr==ff:ff:ff:ff:ff:ff)"
IP Layer:
could be tricky, as the IP Broadcast can be 255.255.255.255 or the highest IP in your IP Network.
So if you have an /24 netmask in a network e.g. 192.168.78.* the broadcast is 192.168.78.255
Therefore the filter would be:
!(ip.addr==192.168.78.255)
of course, you can also use matches filter, which does not need to define the network address like "192.168.78." :
"!(ip.host matches ".255$")" for a /24 network.
Hope this helps
Cheers
Henrik
Homework assignment?