This is the 9439th most frequent Polish word.
waldka
"Waldka" is not a standard Polish word. It might be a misspelling or a diminutive form of "Waldek," a nickname for "Waldemar," a male given name.
This usage of 'waldka' is in the accusative case, referring to the direct object of the verb 'widziałem' (I saw). 'Waldek' is a proper noun, and 'waldka' is its declined form.
Waldka widziałem w parku wczoraj.
I saw Waldek in the park yesterday.
Here, 'waldka' is in the genitive case, used after the preposition 'dla' to show possession or intended recipient.
Podarowałem prezent dla Waldka.
I gave a gift to Waldek.
In this sentence, 'waldka' again appears in the accusative case as 'Waldek' is the object being searched for.