You might not know shinola ...
Shinola is a brand of wax shoepolish that was available in the early- to mid-20th century. The original trademark was filed in 1929 by '2 IN 1-SHINOLA-BIXBY CORPORATION', New Jersey.
Doesn't know shit from Shinola
Its immortality in colloquial English comes from its use in the alliterative
phrase [He] doesn't know shit fÂrom Shinola. Implied is that shit and Shinola, while superficially similar in appearance, are entirely distinct in the effect they produce when brought into contact with shoes, specifically in regard to the navigational hazard presented by piles of the former substance. One who fails to distinguish one from the other is therefore ignorant or of low acuity.
The phrase first became widely popular during World War II. The 1979 Carl Reiner film The Jerk includes a memorable demonstration of the phrase.
Similar meaning can be found in the expression, doesn't know his ass from his elbow, or the variant, doesn't know his ass from a hole in the ground.