How to get the value from ion-select option

There were several things that together caused that error. The first change there is that instead of using the click event like this:

(click)="optionsFn(item);

You should use the ionChange event that Ionic exposes like this:

(ionChange)="optionsFn();"

Also notice that since you use the [(ngModel)]="place" to bind the select element to one of your component's properties, you don't need to send the item as a parameter, because this.place will be the selected item when the ionChange event is triggered.

That's why your optionsFn method would look like this:

public optionsFn(): void { //here item is an object 
    console.log(this.place);

    let item = this.place; // Just did this in order to avoid changing the next lines of code :P

    this.product_option_value_idOp = item.product_option_value_id;
    this.priceOp = item.price;
    this.salespriceOp = item.salesprice;
    this.quantityOp = item.quantity;
    this.skuOp = item.sku;
    this.nameOp = item.name;
  }

Use (ngModelChange) instead of (click) event.

(ngModelChange)="optionsFn()"

whenever the model value changed the ngModelChange will automatically call the relative function.

<ion-item>
  <ion-label>place</ion-label>
  <ion-select [(ngModel)]="place" (ngModelChange)="optionsFn(item)">
      <ion-option value="item" *ngFor="let item of options">{{item.name}} &nbsp;&nbsp;{{item.price}}</ion-option> 
  </ion-select>
</ion-item>