From the VPN interface on the PE router, you can ping the VPN or loopback interface on the directly connected CE router.
From the VPN interface on Router PE1 (VPN1), ping the VPN interface, fe-1/1/0.0, on Router CE1:
user@vpn1> ping 192.168.192.4 interface
fe-1/1/0.0 local 192.168.192.1 count 3
PING 192.168.192.4 (192.168.192.4): 56 data bytes 64 bytes from 192.168.192.4: icmp_seq=0 ttl=255 time=0.866 ms 64 bytes from 192.168.192.4: icmp_seq=1 ttl=255 time=0.728 ms 64 bytes from 192.168.192.4: icmp_seq=2 ttl=255 time=0.753 ms --- 192.168.192.4 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.728/0.782/0.866/0.060 ms