Here's what I can tell you based on the wiki:
Sam Darnold suffered a hip injury in the first quarter of Week 1 against the Patriots and was ruled out after just one drive. Drew Lock stepped in and led the Seahawks to a 13-10 win (from the Drew Lock page).
As for Week 2 — the wiki doesn't have a definitive update yet on whether he'll miss the game. The Seahawks got "positive news" on the injury, but they also "aren't in the clear yet" (per the Drew Lock page referencing a Sept 10 article). On the Mayo Media Network, one analyst noted hips "are a problem" for a veteran like Darnold, suggesting it could linger.
Bottom line: No official Week 2 decision is recorded in the wiki yet. Drew Lock could be a short-term streaming option if Darnold sits, but keep an eye on Seahawks injury reports as the week progresses.