The two most important places are the beginning and the end of the "Mother Road."

Once you leave Chicago, an important stop would be the "Route 66 Hall of Fame and Museum" to get your bearings -- https://www.visitpontiac.org/2192/Route-66-Museum

Before you start, however, you should avail yourself of these two resources:

https://www.goodreads.com/book/show/831180.Route_66 (available many places)
and
https://www.amazon.com/Here-Route-Ross-Jerry-McClanahan/dp/0983935904/ref=pd_lpo_sbs_14_t_0?_encoding=UTF8&psc=1&refRID=GQFSG0MARFYAJYNKFAJY

Nevertheless, there is nowhere along the way that doesn't provide ample opportunities to take memorable photographs.