1. You can look up registered TradeMarks,
2. Common law trademarks, should be popular enough that you've heard about them;
3. Typos of generic are one thing and generally are not an issue if used correctly,
4. TM typos are another issue, which goes into the realm of TM issues.
You may gain some general knowledge by doing research here, and other forums sites. Reading domain TM decisions. If you are really concerned with a potential legal issue you should consult with a qualified IP lawyer especially one who specializes in domains.
There are some issues, which are quite obvious though, lets say you want to start a web-site with the domain "BicycleRiding" about bicycle riding.
Good luck! As mentioned previously these are my thoughts only. For professional advice consult a lawyer.