How to add pilot in ofdm symbol in Gnuradio?

Dear all,

Thanks in advance.
I am currently using Gnuradio 3.6. I cannot see any pilot sub-carrier is
used in ofdm benchmark example. I want to use pilot to trace the phase
offset in each symbol. Is there any example or project that has already
implemented pilot both in sender an receiver? Appreciate your great
help.

Best,
Kay