Can I use Cinccino's "Make Do" Ability if there are no cards in my deck, just to discard a card?
No, you can't use Make Do if there aren't any cards left in your deck.
Source: Sword & Shield FAQ (2020-01-24), TPCi Rules Team (2020-02-06)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH1_147
SWSH1_147
SWSHP_SWSH009
SWSHP_SWSH009