wijmo.angular2.chart.annotation is an external TypeScript module that can be imported to your code using its ambient module name. For example:

import * as wjAnnotation from 'wijmo/wijmo.angular2.chart.annotation';
import * as wjChart from 'wijmo/wijmo.angular2.chart';
 
@Component({
    directives: [wjChart.WjFlexChart, wjAnnotation.WjFlexChartAnnotationLayer,
           wjAnnotation.WjFlexChartAnnotationCircle, wjChart.WjFlexChartSeries],
    template: `
      <wj-flex-chart [itemsSource]="data" [bindingX]="'x'">
          <wj-flex-chart-series [binding]="'y'"></wj-flex-chart-series>
          <wj-flex-chart-annotation-layer>
              <wj-flex-chart-annotation-circle [radius]="40" [point]="{x: 250, y: 150}"></wj-flex-chart-annotation-circle>
          </wj-flex-chart-annotation-layer>
      </wj-flex-chart>`,
    selector: 'my-cmp',
})
export class MyCmp {
    data: any[];
}