Hello,
First you should config the dhcp on the 3945.
And on the Nexus3048 you should:
n7000(config)feature dhcp Enable the “dhcp” feature first!
n7000(config)ip dhcp relay Enable the “relay” functionality in global configuration
Enable the DHCP Relay on the Interface:
n7000(config)# interface vlan 10 (for example)
n7000(config-if)# ip dhcp relay address 10.10.10.10
show ip dhcp relay address interface vlan 10