The simplest way is to run tshark
on the client with options to print rpc response times:
$ tshark -i any -f "port 2049" -Y rpc -Tfields \
-E separator=/t -E header=y \
-e frame.number \
-e rpc.repframe \
-e rpc.time
-e ip.src -e ip.dst \
-e nfs
The output will be something like:
frame.number rpc.repframe rpc.time ip.src ip.dst nfs
Capturing on 'any'
3 x.x.x.x y.y.y.y Network File System, Ops(1): SEQUENCE
4 3 0.000593460 y.y.y.y x.x.x.x Network File System, Ops(1): SEQUENCE
8 x.x.x.x y.y.y.y Network File System, Ops(1): SEQUENCE
9 8 0.000797399 y.y.y.y x.x.x.x Network File System, Ops(1): SEQUENCE
The rpc.time in the reply frame is the difference between sending a request and receiving the reply.
NOTE: the options and output may be different depending tshark version.
Alternatively, you can just collect network traffic with dumpcap or tcpdump and analyze it with the wireshark.