Has Ash ever appeared on any Pokémon TCG cards?
As the Pokémon TCG follows the console games rather than anime, Ash was never a star in the TCG (because he was never in any console game). However, to commemorate few films in Generations III and IV, few promotional cards depicting Ash's Pokémon were released (along many other Owner's Pokémon originating from the films), although all are Japan-exclusive. No Trainer card named just Ash exists.


Pokémon: Destiny Deoxys (M07)


Ash's Torkoal

inserted in a children magazine


Ash's Treecko

Pokémon: Lucario and the Mystery of Mew (M08)


Ash's Grovyle
Ash's Phanpy
Ash's Swellow

Pokémon Ranger and the Temple of the Sea (M09)


Ash's Aipom

Pokémon: Arceus and the Jewel of Life (M12)


Pikachu 
Pikachu  LV.X
Staraptor 



As @JonathanJ mentioned in comments, there is also a card named Ash-Greninja  depicting a Bond Phenomenon Greninja originating in Gen 6 anime. It was released in both Japanese and English, but only the second Japanese print features a picture of Ash.

As @Thunderforge mentioned in comments, in April 2017 a new Japanese-exclusive subset named Ash vs Team Rocket Deck Kit was released, based on Alolan episodes of anime. Some artworks of Pokémon that Ash owns also depict himself. The subset also includes the first Trainer card with Ash in its name.


Rowlet
Ash's Pikachu 
Tauros
Ash's Friendship