Can a wife be given the sotah warning today?
You can, but doing so will only cause problems.
In short, if a person’s wife is secluded with another man, she does not become forbidden to her husband. However, if she was forewarned not to do so and she is secluded with that man, she becomes forbidden to her husband (whether or not she actually did anything with him) until she is given the sotah-test. Since the test is not done nowadays, she simply becomes forbidden to him and the marriage is over.
I know we can’t give her the drink today, but with the warning she would still lose her kesuba if she violated the warning.
I don’t know the answer to this one. For example, if he decided he didn’t want to submit her to the test (for whatever reason), she keeps the kesubah. If she refuses to drink, she loses it. Here, it is neither him nor her who causes the test to not be done and, therefore, end the marriage. My *guess* would be that she does lose the kesubah, but I can’t state that I know that for a fact without doing further research.
The Wolf