I would like to know the difference between 同一 and 同じ. They both mean 'the same'.
Please feel free to provide example sentences so I can see clearly the difference.
The conclusion is practically same with this post, which @l'électeur has linked. These two words have the same meaning except that 同じ is like same and 同一 is like identical. 同一 is just another way to say 同じ in a more bookish, formal, or rigid manner, unless otherwise defined.
Note that some fixed expressions such as 同一人物 may not sound overly formal, and could be used in quite casual talks to mean "(identified as) the same guy".