https://help.ui.com/hc/en-us/articles/204960094-EdgeRouter-Configuration-and-Operational-Mode#:~:text=If%20you%20wish%20to%20run,Mode%2C%20use%20the%20run%20command.
If you wish to run an Operational Mode command from while in Configuration Mode, use the run command.
https://www.juniper.net/documentation/en_US/src4.10/topics/task/operational/cli-modes-switching.html

Ref: Benefits of CoS | Junos OS | Juniper Networks
"Benefits of CoS
...
CoS features allow a Juniper Networks device to improve its processing of critical packets while maintaining best-effort traffic flows, even during periods of congestion.
...
CoS dedicates a guaranteed minimum bandwidth to a particular service class by reducing forwarding queue delays.

According to the Juniper Networks JNCIA-Junos Study Guide, "Neighbor Discovery Protocol (NDP) is the IPv6 equivalent of ARP in IPv4. It is responsible for learning a neighbor's link-layer address and determining the reachability of a neighboring device." Reference:
So, the Neighbor Discovery Protocol (NDP) is responsible for learning an IPv6 neighbor's IMAC address.