Answer:
You use a knife to slice my head but you weep beside me when I am dead
Drop me and the world will shatter. You can always find me where you empty your bladder.
I'm as simple as a circle worthless as a leader; but when I follow a group their strength increases tenfold. By myself I'm practically nothing.
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
I'm blue at day and black at night. I do contain some creatures born and died. What am I?
If you can get this professional's attention you can get where you need to go for a price.