By default, a chart in SSRS will automatically position the labels on the X-axis as it best fits. However, one of these options includes hiding labels when the chart feels there are too many to show. As you can guess, this is not always what we want.
When opening up the axis properties for the X-axis on a column chart you get the Category Axis Properties screen. Like all other property screens, this is also one with several pages. You see that one of the pages is called Labels and as you want it to show all labels, that’s were you start looking. Well, stop looking, that’s the wrong place. The option that you need is located in the first page, the Axis Options, and its called Interval. This is the interval between each label on the axis, and by default it is set to Auto. As we want all labels, change it to 1.
I changed the direction of the labels as well, to rotate 90 degrees: