format

A format string or function for overriding the value for displayed for the data point (if enabled).

Format string example:

seriesSettings: {
    donut: {
        dataPointText: {
            enabled: true,
            format: "{point.y:n1}"
        }
    }
},

Format function example:

seriesSettings: {
    donut: {
        dataPointText: {
            enabled: true,
            format: function(point, chart) {
                return point.y + " (" + point.x + ")";
            }
        }
    }
},

This setting is demonstrated in the following example.