Usage:

# journalctl -fu {service name}

Example:

# journalctl -fu ntpd
-- Logs begin at Fri 2020-01-17 07:53:02 KST. --
Feb 24 19:35:47 SBC1-1 ntpd[25165]: Listen normally on 9 lo ::1 UDP 123
Feb 24 19:35:47 SBC1-1 ntpd[25165]: Listen normally...
# grep processor /proc/cpuinfo | wc -l
40