My second molar feels loose and sore 6 days after my wisdom teeth surgery. is this normal? and why?

Can be normal: You are probably missing the distal wall of bone on that second molar following the extraction. In addition, the act of extracting the wisdom tooth may have loosened up the second molar during the procedure. Everything should tighten up as the bone fills in and as the stress on the second molar subsides. Speak to your surgeon if after a couple of weeks you don't feel better.

Best to inform: Your surgeon and dentist so that they can document this and keep an eye on that tooth. It can certainly be within normal limits to experience this post wisdom tooth removal. The mobility and sensitivity should lessen over the next several weeks to months once the hard tissue and soft tissue become re-established in the region behind the molar in question - restoring support and "insulation".