>My question is - how can I access this _fieldID in my code?
>I need to check _fieldID for some specific string, what would be my syntax?

As I can see in source code _fieldID is private field used by public property FieldId of SqlWhereBuilderCondition class

private string _fieldId = "";
///

/// The string identifier for the SqlWhereBuilderField used in this condition
///

public string FieldId
{
get {return _fieldId;}
set {_fieldId = value;}
}


You can access this property simply

mySWBuilder.Conditions[0].FieldId

Maybe I misunderstand your goal?