Super common date and absolutely no value in that condition. I am not even sure its genuine.
I would never recommend cleaning coins, but for that dog I would make an exception as it can't possibly get any worse.
The 1938 penny had 121 million minted and has no catalogue value until its EF at £1 and £5 UNC. In that condition its damaged poor and not even worth the copper melt of 5 pence.
1938 is the most common date of all the King George VI pennies and only the years of 1966 and 1967 saw more predecimal pennies minted.
Sorry to bear this news, but it will save you the energy and effort.