I am working on blue card in Germany and have recently started a YouTube channel .Can I earn small amount from channel Monetization through Google addsence.Do I need to take any permission for such small earnings 100 euros per month and register this as business
In general taxation, you should come to post this at LAW sites.
But to be clear the taxation for business and personal is different, you have personal income but not as business as you are working for another company but not legal (there is no data stating you are working on that company).
Germany has a law of tax stated 'The first €9,169 (or €18,338 for married couples with a joint return) you earn each year in Germany is tax-free. Any amount earned ABOVE €9,169 is subject to income tax.' <this is for personal income tax.
if you have an income of only €100 a month * 12months = €1200 that was below €9169. You will not get taxed, just add it to your personal income. But if you proceed as a business it will make you more difficult because you need to apply for the business license, and business tax is more difficult to understand without a proper tax code.