Shortcut to open dialog to insert icon

When I google this I can't find it. But sometimes when I'm in the console and I'm fiddling around a certain key combination triggers a dialog to appear. In the dialog you can choose an icon to insert. Just like the icons you can use in for example whatsapp. I tried al lot of combinations but I can't seem to find the right pair. The three times it happend it happend on accident. What is the key combination to open this icon dialog?