Click the three dots (top right).
Go to Bookmarks > Show Bookmarks Bar.
(Alternatively, press Ctrl, Shift and B together)
Hint: You can get far more than 6 sites across the top of your window if you shorten their names. (I'm using Slimjet, which is a Chrome variant, and I've got 20 up there!). For example, if you change 'YouTube' to 'YT' and 'Amazon' to 'Amaz', there will more space for additional sites. To do so, simply right-click on the name of a site and select 'Rename'.