can i download my raw file from my Nikon d5600 to Aperture?

No, Apple stopped supporting Aperture about 3 years ago, and do not update its RAW database. However you can download Adobes DNG converter, it is free. This will convert your Nikons .NEF files to Adobes .dng format, when you have done that you will be able to import them and edit them in Aperture.

Adobe - Adobe Camera Raw and DNG Converter : For Macintosh : Adobe DNG Converter 10.4

Which version of MacOS X are you running on your Mac?

The Nikon d5600 is supported natively in macOS 10.13.x High Sierra, but nit in the earlier versions of MacOS X.

That means, if your Mac is running High Sierra, you can import the photos to Photos for Mac and convert them in Photos to to TIFF files on export. Import the TIFF files to Aperture.

The DNG converter will give you a better compression, however.