Well, for Clip Studio Paint EX, I get the Windows 10 system to generate it for me. I go into Add Text mode in Clip Studio. I press simultaneously: Windows key + period key (full stop key). The emoticons window pops up. I click on the heart symbol at bottom right, which is the shortcut to get to the Symbols section of the emoticons window. I scroll through the symbols section until I get to a row which contains the copyright symbol. Click on it and it shoul appear in your text line in Clip Studio Paint.