Usage:

# /sbin/ip -6 tunnel show [<device>]

Example:

# /sbin/ip -6 tunnel show mode any
ip6tnl0: ipv6/ipv6 remote :: local :: encaplimit 0 hoplimit 0 tclass 0x00
¬ flowlabel 0x00000 (flowinfo 0x00000000)
ip6tnl1: ip/ipv6 remote fd00:0:0:2::a local fd00:0:0:2::1 dev eth1 encaplimit 4
¬ hoplimit 64 tclass 0x00 flowlabel 0x00000 (flowinfo 0x00000000)

NOTE: If you don't include "mode any", only IPv6-in-IPv6 tunnels are displayed.