How much I can earn from mobile game?

There are a lot of factors that will play into this.Major factor is number of downloads. For a typical game with roughly 1500-2000 downloads a day, that game generates $30-$50 per day. 

The fluctuation will happen on the weekends when more people have free time and are checking out new games. So the money then is always higher.  

In-app purchases can also increase revenue as an additional revenue stream. So in theory if we can convert 2000 downloads a day to in-app purchasers, the revenue stream will be much higher.Even if just say 5% spend $2 that's $200 more revenue on a very small number of downloads.According to the big boys like King and Supercell, they are averaging between $1.49 and $36.99 average purchase!

Another factor is holidays. We noticed right after Christmas the graph skyrocketed on downloads. This most likely was because of devices people got for Christmas. So holidays are a great time to push out new titles or update old ones.  

Then if you are lucky maybe you can create a hit like Flappy Bird and generate $50,000 a day.