For example, there is a domain "TOGOOD.COM" ... which is already registered... I am booking a new domain today "2GOOD.COM".......so will it be right to do???
2good.com is taken a long time as well. But generally the answer to your question - depends on the name.
Both 2 (to or too) and 4 (for) can be good matches with good keywords or combinations. But the problem is it's very rare nowadays. A bit easier with trending words (but everything is easier with trending words).
What I meant was that "TOOGOOD.COM" (all ready book) .....book is there,,,,, I am booking 2GOOD.COM (fresh new domain).. will it remain true......?? The meaning of both the names is same...because it will be correct to book in the same way.