Protocol instance objects have a Tcl type field of proto_inst. You can use the get_objects Tcl command to locate protocol instances in or under a specific scope.
Use the Following Command to Locate All Protocol Instances in the Design:
get_objects /* -r -filter {type==proto_inst}
Use the Following Command to Locate All Protocol Instances in a Scope:
get_objects <Design scope hierarchy>/* -filter
{type==proto_inst}
Use the Following Command to Locate All Protocol Instances in or under a Scope:
get_objects /system_tb/base_mb_wrapper/base_mb_i/* -r -filter
{type==proto_inst}