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Depending on the type of APIC you have, it will either come with a VIC1225 for SFP+ connections or a VIC1225T for regular RJ-45 copper connections. Both connect to the front panel ports of the leafs and operate at 10G. the VIC1225T connects only to a 93128 with CAT6 or CAT6A whereas the VIC1225 connects only to a SFP+ leaf like the 9396 you mentioned via 10G-SR optics or TwinAx copper cables with the built in SFP+ connector.
In order to connect the Leafs and the Spines together via the uplink ports on the GEMs toward the spines, 40G must be used. The QSFP-40G-SR4 you mentioned should work and is supported on the ACI GEMs and spines. That SFP supports only MPO/MPT terminated multimode fiber which i believe has 12 fiber strands inside and is how the 40Gig speed is achieved.
Cisco also has a Bi-Di optic (QSFP-40G-SR-BD) that uses standard multimode fiber terminated with LC connectors as well as some pre-terminated cables with the QSFP built in or "direct attached" such as the QSFP-H40G-AOC
I hope this helps, here are some reference websites
http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/datasheet-c78-730160.html
http://www.cisco.com/c/en/us/products/collateral/cloud-systems-management/application-policy-infrastructure-controller-apic/datasheet-c78-732414.html
http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/datasheet-c78-729404.html
http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/white-paper-c11-729987.html
http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/white-paper-c11-729493.html
http://www.cisco.com/c/en/us/td/docs/interfaces_modules/transceiver_modules/compatibility/matrix/40GE_Tx_Matrix.html
