The week number will be displayed in the first header row if you use

dps.cellGroupBy = 'Week';

You can always override the onBeforeTimeHeaderRender() to customize the header HTML:

		@Override
		public void onBeforeTimeHeaderRender(BeforeTimeHeaderRenderArgs ea) throws Exception {
			ea.setInnerHTML("Week " + Week.weekNrISO8601(ea.getStart()));
		}