A Jupyter notebook only displays the result of the last expression in any given cell. The other lines of code are executed, but their results are simply not displayed unless they call an explicit output function.
If you want to display both strings, you can (a) put then in separate Jupyter cells, or (b) manually call display (the multimedia analogue of println) on the things you want to show, e.g.
Alternatively, if you are just trying to show some text, you don’t need to execute Julia code at all — just change the cell type to “Markdown” and enter Markdown text with equations in $...$:
The Separation of Variables has quotes. If I remove the quotes, nothing is displayed at all after the cell. How can I display ‘Separation of Variables’ and the equations without any quotes?