Redundant explicit property name in C# warning

My question are 1) for this anonymous object parameter where I now remove the property names so I don't get the Resharper warnings anymore, how does it know what the property names are since they are passed by value?

The names are inferred (by the compiler) from the expressions. This only works when you're using a field or property (not a literal or a method for example). This is in section 7.6.10 of the C# language specification.

2) what is best practice having the property names in or not. Having them not in is not very readable and in code samples they are specified so I would imagine having them in is better rather than removing it

If it's more readable for you and your team to always include the name, then go ahead and do so. For other people, it may feel a little redundant. Just adjust your R# settings to fit your local conventions.

Your argument that "in code samples they are specified" is specious though - there are some examples where they're specified and some where they're not. I suspect you'll find a mixture even within particular example providers (e.g. in MSDN).

When you set up your propertyNames object you're creating an instance of an anonymous Type - when you do that you can leave out the property name if it's the same as the property from which you're assigning the value. That's why ReSharper says the names are redundant.

Explicitly stating property names when you don't have to is personal preference; once you're familiar with the above convention I don't think it harms readability.