To get 2 lines put a '\n' where you want the line break: "Q1 BTI vs, POR\n(with open po's from 2015)"
To change the font size of the second line, I use the render event to get the text element of the second line and manipulate it. Set the x coordinate to the center of the chart, change the text-anchor to middle and then get the second element and change its font size:
$("#chart").kendoChart({ title: { text: "Q1 BTI vs, POR\n(with open po's from 2015)", font: "20px sans-serif", color: "rgba(55,55,55,0.999)" }, series: [ { data: [1, 2, 3] } ], render: function(e){ $('[fill="rgba(55,55,55,0.999)"]').attr("x", e.sender.element.width() / 2).attr("text-anchor", "middle")[1].style.fontSize = "12px"; }});