If a tRNA molecule has an anticodon which reads Aug what was the codon of the mRNA molecule

The answer is UAC.

In the RNA, base complements are adenine - uracil (A-U) and guanine - cytosine (G-C). So, when in the process of translation, anticodons of tRNA pairs with codons of mRNA, the complementary bases will pair. So, adenine in tRNA will pair uracil in mRNA (A → U), uracil in tRNA will pair adenine in mRNA (U → A), and guanine in tRNA will pair cytosine in mRNA (G → C):

tRNA: A U G

mRNA: U A C