Using string formatting

func typeof(v interface{}) string {
    return fmt.Sprintf("%T", v)
}

Using reflect package

func typeof(v interface{}) string {
    return reflect.TypeOf(v).String()
}

Using type assertions

func typeof(v interface{}) string {
    switch v.(type) {
    case int:
        return "int"
    case float64:
        return "float64"
    //... etc
    default:
        return "unknown"
    }
}