[Vuejs]-Transmit event to parent component using btable

Just transmit it to the parent.

<modal_delete-subnet :subnet="data_subnets.item" @delete-subnet="$emit('delete-subnet', $event)"></modal_delete-subnet>

Or if you have your delete handler in SubnetTable, handle it here.

<modal_delete-subnet :subnet="data_subnets.item" @delete-subnet="deleteHandler"></modal_delete-subnet>

export default {
  ...
  methods: {
    deleteHandler(e) {
      console.log(e)
      // delete actions here
    },
  },
  ...
}