If a request is being sent via unicast or broadcast, would that show in the destination or source address?

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"Sent" is the key word here; the destination MAC address is the MAC address to which a packet is being sent, so that's the address to check. The source MAC address just says who's sending it; they can send broadcast or unicast packets, so the source address can't tell you whether it's broadcast or unicast.

By the way, there's another possibility - multicast - so:

• if the destination MAC address is ff:ff:ff:ff:ff:ff, it's broadcast;
• otherwise, if the "IG bit" is set, meaning it's a group address, it's multicast;
• otherwise, it's unicast.

The IG bit is the low-order bit of the first byte, so if, for example, it's 0x80, it's unicast, as that bit is clear, but if it's 0x81, it's multicast, as that bit is set.