Is there a way to view known blueprints without an empty upgrade slot?

Not for the multi-tool (on PS4).

All products that can be constructed in the suit can also be constructed in the ship, so if you have no free slot in one you can at least check product blueprints in the other. (Not so for upgrades, of course.)

On the plus (?) side, enhancement blueprints seem to be pretty limited (at least as far as I am into the game) so if you get only duplicate suit, ship, and multi-tool blueprints 100 times in row, it's a good bet you've found everything.

Of course that still doesn't help if you're just trying to check the ingredient list for an upgrade, which is where the internets come in. :)