First biopsy of a solitary nodule in the right lung, close to oblique wall, without cancer cells. Doctor sending me to different respirologist, why?

Not clear. Not exactly clear of situation. Presuming you are being sent to another pulmonologist for another diagnostic attempt/biopsy? As noted, the details: age, risk factors, symptoms, characteristics on the ct, on pet scan would impact degree of suspicion of cancer and suspicion maybe first biopsy false negative. Sounds like your doctor is looking out for you.
Need more informatio. Age, tobacco history, where do you live, where have you traveled, any symptoms that led to discovery of the nodule, other medical problems, recent illnesses. What does it look like on the ct, have you had a pet scan. I could go on for a while, but it sounds like your doc wants a second opinion. We don't have the benefit of all that information and more to answer your question.