Which field in an Ethernet II frame performs the same function as the DSAP field in an 802.3 Ethernet frame?

The Start of Frame delimiter (SFD) signals the beginning of the frame to receiving hardware - it plays no role in identifying the upper-layer protocol.

The EtherType field in an Ethernet II frame is a 2-byte field that identifies the Layer 3 protocol encapsulated in the frame payload (for example, 0x0800 for IPv4 and 0x0806 for ARP). This is functionally equivalent to the DSAP field in the 802.3 LLC header, which also identifies the destination upper-layer service or protocol that should process the incoming data.

The Frame Check Sequence (FCS) is a 4-byte CRC trailer used for error detection, not for protocol type identification.

SNAP (Subnetwork Access Protocol) is an extension header used within 802.3 LLC frames to allow EtherType-style protocol identification, but it is not itself the counterpart to DSAP.

LLC (Logical Link Control) is the sublayer and header structure that contains DSAP and SSAP fields in 802.3 - it is the broader container, not the functional equivalent of DSAP.