How can I input punctuation marks like ellipsis?

Solution 1:

I think what you are looking for is in the Unicode composition section of the Ubuntu documentation for the ComposeKey. The next bit is based on the instructions in that section.

Another means to enter non-keycap characters is to enter them as a Unicode character number.

• Press ShiftCtrl+U.
  
  Release U while continuing to hold down ShiftCtrl.
  
  Enter the four hexadecimal digit (0123456789abcdef) number for the Unicode character code point. (An underlined u followed by the number will display as you type.)
  
  Release ShiftCtrl.

• Another alternative is to press (and release) ShiftCtrl+U. An underlined u is displayed.
  
  Enter the hexadecimal Unicode character code point
  
  Press Return.

I used the instructions above to create this string: ‘some text’ … (Ta-Da!)

For whatever its worth, I found this by looking at this answer to the question "How can I type special characters like ë?".

This question was at the top of the list of links "Related" to your question. The Related links list is always present in the right hand sidebar of any question on a Stack Exchange site.