One way to figure out whether the peptides in your Skyline document can be found in another proteome is to use the:
Refine > Associate Proteins
menu item and then provide the FASTA file of your other proteome and see whether any of the peptides got moved into a protein from the provide FASTA, or were moved into the "unmapped" peptide list.

The usual way to get the peptides from the 7 protein standards into the Skyline document is to create a FASTA file with those 7 protein sequences.
Then you can insert those into the document using the "File > Import > FASTA" menu item or "Edit > Insert > FASTA".

There is another way to check for protein uniqueness involving going to the "Digestion" tab at "Settings > Peptide Settings" and setting up a background proteome. Once you have a background proteome you can use the "Edit > Unique Peptides" menu item. However, "Refine > Associate Proteins" is probably easier.

By the way, I recommend using Skyline-daily instead of Skyline 24.1 for this because in Skyline-daily we changed it so Associate Proteins would find non-tryptic peptides in the provided FASTA file. In Skyline 24.1, a peptide that was present in the FASTA file but where one or both ends was not a tryptic cleavage site would end up being moved to the "unmapped" peptide list.

You can install Skyline-daily using the "Skyline-daily (beta)" button on the main Skyline page:
https://skyline.ms/project/home/software/Skyline/begin.view
-- Nick