My company is going to send me to Dresden,Germany to support my customer. I have a Schengen visa and am expected to stay there for about 3months. Is there tax payable for me? Who can provide the official tax office website in Germany?

I assume you are a U.S. citizen.

If the source of your 3-month income comes from INSIDE Germany, then the income will be subject to German income taxes.

If the income is sourced from the U.S. it is EXEMPT from German taxes.