Can I Ask People to Subscribe to Enter My Giveaway?

Not as a way to earn an entry. You can ask viewers to subscribe in your video, but you can't reward it.

We removed the Subscribe to a YouTube Channel Action to keep creators within YouTube's Fake Engagement Policy. Comment on a Video and Watch a Video on YouTube went for the same reason. The policy lets you encourage people to subscribe, like or comment, and bans content that exists only to reward engagement.

Here's what you can use instead from our YouTube Actions:

• Visit a YouTube Channel sends entrants to your channel, where they decide for themselves whether to subscribe. Switch on Require Authentication so you know who they are when you draw winners.
• YouTube Entry lets people enter by logging in with YouTube.
• Submit a YouTube Video works for video contests.