A clever clogs is someone who always has an answer. This could be in a classroom situation but more often, it is a negative description of someone who always has a smart remark to make - so they are quite irritating.
A clog is a shoe made of wood that was popularly worn by workers in the northern English mill towns in the 19th century. It is also a shoe synonymous with Holland, but quite why clogs and clever go together, I can’t say. Maybe I’m not clever enough.