columns click function,can not get "this" about gantt-elastic

[neuronetio]

Events are not binded to Events c'mon ;) but this inside function in option events for sure are not pointing to your containing component.
This is intended behavior - this is up to you what you bind to your events - you can also use scoped variable in your function to get your component data.
gantt-elastic does not want to know anything about parent component - it should be kind of sandboxed and self contained thing.
I don't know how you mount gantt (as standalone component? as component in other component?) so I can't really help - more code is needed to help.
I suggest to mount via app = new Vue(....) option, so app will contain all your data, and then inside click handler you can use app.lastId data property.

let app;
const tasks ={/*...*/};
const options = {
/*...*/
click({event, data}){
    // app is assigned here for sure because no click event will be fired before vue initialisation,
    // after vue is mounted and start working, click event will be fired, and after vue is mounted app is assigned
    app.lastId++;
}
/*...*/
};
app = new Vue({
  el:'#gantt',
  template:`<gantt-elastic :tasks="tasks" :options="options"></gantt-elastic>`,
  components: {
    ganttElastic: GanttElastic
  },
  data() {
    return {
      tasks: tasks,
      options: options,
      lastId:16,
    };
  }
});

[neuronetio]

You can also define function before and bind it to your app (javascript is really elastic and I like it for this :) ).

let app; // for now let it be here and wait for assignment
function myClickHandlerBluePrint({event, data}){
  this.lastId++;
}
const myClickHandler = myClickHandlerBluePrint.bind(app);
const options = {
/* ... */
  click: myClickHandler, // WHAAAAAT :O ?
/* ... */
};
app = new Vue({  // let assign vue instance to app variable
/* ... */
data(){
  return {
    tasks,
    options,
    lastId:16,
  };
}
/* ... */
})