Hello, I am planing to open new site. This should get 20-30K pageview and 50$ per day from G. Adsense. What sould be this site's content?
I think its odd that you're asking us for ideas on content. You should create content from what you're good at and won't be bored by, that way you'll be interested and so will other readers.
Well, I suppose some type of news site would be the best for making money from ads, since the content would be varied and users might want to follow up a story with one of the relevant links on there. But news sites are hard to get successful since they have to be updated every few seconds. Or! You could just get loads of random RSS feeds for your website, from various other news sites, ect. Almost no work for you and you would still get page views, I guess.
A suggestion: Publish a theme-based information-jammed content site. The content may deal with your hobby, passion or the field you have some experience in. You could then blend in AdSense. Diversify as you grow. CTPM is a proven concept. (Good content attracts traffic. Pre-selling comes next, followed by monetization.)
This is not really the best way to start a website. You should first think of something you enjoy and then you can figure out you are going to monetize it.