How do I use DateTime.TryParse with a Nullable<DateTime>?

As Jason says, you can create a variable of the right type and pass that. You might want to encapsulate it in your own method:

public static DateTime? TryParse(string text)
{
    DateTime date;
    if (DateTime.TryParse(text, out date))
    {
        return date;
    }
    else
    {
        return null;
    }
}

... or if you like the conditional operator:

public static DateTime? TryParse(string text)
{
    DateTime date;
    return DateTime.TryParse(text, out date) ? date : (DateTime?) null;
}

Or in C# 7:

public static DateTime? TryParse(string text) =>
    DateTime.TryParse(text, out var date) ? date : (DateTime?) null;

DateTime? d=null;
DateTime d2;
bool success = DateTime.TryParse("some date text", out d2);
if (success) d=d2;

(There might be more elegant solutions, but why don't you simply do something as above?)

Here is a slightly concised edition of what Jason suggested:

DateTime? d; DateTime dt;
d = DateTime.TryParse(DateTime.Now.ToString(), out dt)? dt : (DateTime?)null;