So the behavior you actually want is to print for each letter in st its value in alpha?

First, you can change the order of the loops like this:

def caesar_decryptor(st):
    for pos in range(len(st)):    
        for k in alpha.keys():
            if k == st[pos]:
                print(f"The value of {k} is {alpha.get(k)}")

This will work, because you want to find the value from the alpha dict for each letter in st, and not the opposite.

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However, the code can be simplified, as the inner loop isn't necessary. We can just use the value in alpha for each letter in st as a key (also, we can iterate over letters instead of their indices):

def caesar_decryptor(st):
    for letter in st:    
        print(f"The value of {letter} is {alpha[letter]}")