Hi,
As per the datasheet, CoS including 802.1p and EXP is supported:
QoS Features • Support for 802.1p, DiffServ code point (DSCP), EXP
https://www.juniper.net/assets/fr/fr/local/pdf/datasheets/1000550-en.pdf
https://www.juniper.net/assets/us/en/local/pdf/datasheets/1000551-en.pdf
Cheers,
Ashvin