Cisco have changed the way you configure port or VLAN monitoring on the NX-OS based switches.
You can now configure a maximum of 18 SPAN sessions on a device BUT only two SPAN sessions can be running simultaneously. SPAN sessions are shutdown and enabled using either 'shutdown' or 'no shutdown' commands
Its also a two stage setup process, you have to define your monitoring ports first and then configure your monitoring sessions
Step 1 Step 2 
Configure destination ports in access or trunk mode, and enable SPAN monitoring.switch# config t
switch(config)# interface ethernet 2/5
switch(config-if)# switchport
switch(config-if)# switchport mode trunk
switch(config-if)# switchport monitor
switch(config-if)# no shut
switch(config-if)# exit
switch(config)#
Configure a SPAN session. switch(config)# no monitor session 3
switch(config)# monitor session 3
switch(config-monitor)# source interface ethernet 2/1-3, ethernet 3/1 rx
switch(config-monitor)# source interface port-channel 2
switch(config-monitor)# source interface sup-eth 0 both
switch(config-monitor)# source vlan 3, 6-8 tx
switch(config-monitor)# filter vlan 3-5, 7
switch(config-monitor)# destination interface ethernet 2/5
switch(config-monitor)# no shut
switch(config-monitor)# exit
switch(config)# show monitor session 3