Pipe in attic?
 

I went into my attic and found this pipe with some type of screen or device on the end and am wondering what it is.

Waste drain vent
In modern plumbing, a drain-waste-vent is a system that allows air to enter the plumbing system to maintain proper air pressure to enable the removal of sewage and greywater from a dwelling. Drain refers to water produced at fixtures such as sinks, and showers; waste refers to water from toilets.

Got to have a start point below.

It looks like it may be an automatic air vent from a plumbing fixture. Plumbing fixtures are usually vented through the roof with an open pipe, but if it is difficult to extend an open pipe through the roof, it is acceptable to use an automatic air vent device. Many kitchens have these located in the sink cabinet below the countertop to vent the sink drain, but they can also be used in the attic, when venting through the roof is not convenient. Although, if it is an automatic air vent, it would have been better for the builder to connect the vent to another vent pipe that extends through the roof.

Look up "studor valve".

Well I learned something today with the help of the person that identified this as a studor valve. Note that this is a one way valve and only opens to intake air on demand.

Yep, and they can fail, sticking open or closed. If your sink drain starts to suck air (which will empty the trap creating an open route to sewer gas smell), you know what to check. Also, if there is sewer gas smell in the attic, ditto.