If I kill a Lonely Poro that is alone at a battlefield as part of the additional cost to play Stalking Wolf, do I still get the card draw, or was the Lonely Poro considered not alone when Stalking Wolf was played?

Yes — you still draw 1 from Lonely Poro.

"Alone" is a historical check, evaluated at the moment the Poro dies — not when the trigger resolves, and not after Stalking Wolf lands. When you kill the Poro to pay Stalking Wolf's additional cost, Stalking Wolf is still pending on the Chain and has no board presence, so the Poro dies with no other friendly units at that battlefield and its Deathknell triggers validly (Rule 808.1.d.3; FAQ #373, #9841).

Stalking Wolf finalizing to that battlefield afterward — even to the exact same battlefield — does not retroactively make the Poro "not alone." The trigger resolves and you draw. This is the same logic that lets you play an Ambush unit in response to the Deathknell and still draw.

One caveat: this only works if the Poro was genuinely alone at the moment of death (no other friendly units at that battlefield). If it wasn't, the trigger never fires.