Please help authenticate original Wassily chair or repop  

It looks real to me. does the bottom tube join in the center or or is there a length of tube that attached in two places? not sure about the extra holes in the tubes though. It will probably clean up pretty well but they are a pain in the ass to disassemble and reassemble. 

Greetings.
Your chair is not a Knoll product. 
Nope.
Aunt Mark

FYI: Knoll is not the only company to make them; they were made by Gavina in the 60's and 70's. Knoll purchased he Gavina catalog in the late 70's and now they make them.  

it joins in the center.

it's look like a MARCEL BREUER chair, model B3