What is the simple subject and simple predicate in this sentence?

Simple subject: days Simple predicate: can make

Rain/fog are objects of the preposition "of". They act as modifiers of the word "days" Rain/fog are not the of the sentence.

"Dreary " and "disagreeable" are adjectives modifying "week".

Consider this:

Two days can make a whole week.

Ask: two days of what? Ans: two days of rain and fog

Ask: can make a whole week what? Ans: can make a whole week dreary and disagreeable.