Hopefully the person also sent you a ".sky" file as well.
Typically, you would never open the ".skyd", ".sky.view" or ".skyl" files directly, but, instead, you would tell Skyline to open the .sky file, and Skyline would also end up looking at those other files at the same time.

The usual way to send someone a Skyline document involves using the "File > Share" menu item in Skyline to create a ".sky.zip" file (or sometimes just ".zip") which will contain the Skyline document (.sky) plus whatever supporting files are necessary including the .skyl, .sky.view, etc.
You can use the "File > Open" menu item in Skyline to either open a ".sky" file or a ".sky.zip" (or ".zip") file. If the file is a .sky.zip or .zip file, then Skyline will extract all of the contents to a new folder and open the .sky file.

The .sky.view file contains information about which windows are open in Skyline and where they are on the screen.
The .skyd file contains extracted chromatograms. The format of that file is only understood by Skyline so there are no other tools for looking at it.
The .skyl file contains the Audit Log which you can see using the "View > Other Grids > Audit Log" menu item in Skyline after you have opened the .sky file.

If someone has sent you these files without a .sky file you should ask them to use the "File > Share" menu item in Skyline to create a .sky.zip file which will contain all of the necessary files and ask them to send you the .sky.zip.

If you are having trouble making sense of what you have been sent, you can send the files to us.
Files which are less than 50MB can be attached to this support request. You can upload larger files here:
https://skyline.ms/files.url
-- Nick