Can an apostrophe be added with capital letters?

Yes, an apostrophe can be used with capital letters, particularly in contractions and possessives. For example, "It's John's book" shows a contraction with "It’s" and possession with "John's." Additionally, when indicating possession for a proper noun, you would write "The Smiths' house." The use of an apostrophe with capital letters follows the same grammatical rules as with lowercase letters.