I am not sure that I understand your question.
If you want Skyline to extract chromatograms for fragment ions, you would need to have some numbers in the "Product m/z" column so that Skyline knows which fragment ion to look at in the MS2 spectra.
I guess if you did not care which product m/z Skyline looked at because all you wanted was an MS2 chromatogram that you could click on so that Skyline would bring up the spectrum viewer, you could put any number that you wanted to in the Product m/z column. But, you would need to have a number in that column of your transition list, and that number would need to be different from the number in the Precursor m/z column.
You can also add MS2 transitions to your document by right-clicking on one of the things at the third level of the hierarchy in the Targets tree and choose the menu item "Add Transition". In the Add Transition dialog, you can change the "Monoisotopic m/z" and "Average m/z" values to be different from the precursor, and then Skyline will add a new transition to the Targets tree.
After you have added some transitions, you could tell Skyline to extract chromatograms again by going to "Edit > Manage Results" and pushing the "Reimport" button.
If you have both MS1 and MS2 chromatograms, you might have a hard time seeing the MS2 chromatograms because the MS1 chromatograms have much more signal. You can right-click on the chromatogram graph and choose "Split Graph" so that the MS1 and MS2 chromatograms are drawn in separate panes.
Skyline is not a very good tool for looking at spectra because most of Skyline's features revolve around extracting chromatograms. If you want to look at spectra in your raw files you might have an easier time using the QualBrowser software that comes with Thermo instruments. We also have our own program called "SeeMS.exe" which you can get by installing "ProteoWizard".
https://proteowizard.sourceforge.io/
-- Nick