How to insert the Interpunct character in ubuntu?

Simply press Ctrl+Shift+U, then type "00b7Enter", i.e. the unicode value of interpunct character.

The default way to do this is given in the Ubuntu Help page: The Gtk Dead Key Compose Table. The sequence for the middle dot is: ThirdLevel Chooser + DeadKey-Cirucmflex + period or expanded: AltGr + Shift + AltGr + Shift + ^ + .. This is supposed to work even without changing keyboard options.

Compose key combinations, however, did not work reliably on my system until I set a compose key in the Keyboard Layout.

Settings > Keyboard Layout > Options > Expand Compose Key Position and choose the key you want. I chose RightAlt so now, RightAlt + Shift (now in 3rd level) + Shift + ^ + . inserts the middle dot.

Copy an interpunct · from Wikipedia or anywhere. Paste and save it in a document on your desktop. Copy from there and paste when you need to use it. Or, from your word processing program's toolbar, go to insert, select special character, choose the raised dot (6th row down, 12th over in Microsoft Works), and change the font size to whatever you want it to be. It isn't perfect (it's much lower than an actual interpunct) but it's a little higher than a period. Also the lower case letter l in both wingdings and webdings makes a black dot but it isn't much higher than a period. Lower case h in Marlett makes a similar dot, but quite a bit larger and Marlett keeps inserting a box for a blank space, which is kind of a nuisance. You could type all the upper and lower case keys on your keyboard, then try out each font in your system to see if any of them produce a better looking "interpunct."

Here is a larger interpunct if you would like to copy it for pasting elsewhere: interpunct • interpunct

I use US international layout and I can write the interpunct with AltGR + . (release all the keys) and then the keys that needs the interpunct. For example the interpunct between the two Ls in "Paraŀlel"