I really "need" to get one of my second channels past 1000 subscribers and monetised so I can find out as well. I know each individual channel needs to qualify individually as Andrew has pointed out. I assume they both link to the sam adsense account, and would pay out combined rather than individually.
Also keep in mind, although a channel might get monetisation, it requires a $100 minimum for payout, so you might make $20 one month, $50 the next month and still have to wait a few months until you have made enough for the $100 minimum payout.
I've had a month where I made $99... so of course, I had to wait 2 months so I could get that payout which was a bit of a pain.
Focus on making good content and don't worry about monetisation.
If making money is important to you, get a brand deal or a sponsor. And in that regard, they might be even harsher than your audience in what they expect quality wise from your content, so at the end of the day it's the content that matters, not the monetisation, because you won't be making a lot regardless.
You need to have LOTS of subscribers, like in the 80k+ territory to get anywhere near $1000 a month on adsense alone, and that's not enough to pay rent etc.
So while adsense is a great bonus, have a content strategy and business plan that goes outside of monetisation.
