Can a neck MRI with contrast show any malignant lymph nodes near collarbone or where posterior neck joins the shoulder?

Yes and no . An MRI can do many things, like show if you have enlarged lymph nodes - however in order to determine if they are benign or malignant you would need a biopsy of the tissue in question. I will often order an ultrasound first when evaluating lumps in the neck, and only order MRI if the ultrasound is inconclusive or unable to do needle biopsy. .