1. Asking for the reading (pronunciation) of a character or compound:
この[字/言葉]の読み方は何ですか？
この[かんじ/ことば]のよみかたはなんですか？
Use 字 for single characters, and 言葉 for compound words made up of more than one character.
Keep in mind that when asking about single characters, there can sometimes be LOTS of readings, both おん readings and くん readings. Unless the single character is also a independent word, like 日（ひ, day or sun）for example, I would avoid asking about single characters myself.
2. Asking someone to write a character or word in hiragana or katakana:
この[字/言葉]はひらがなで書いてもらいませんか。
この[かんじ/ことば]はひらがなでかいてもらいませんか。
You can change ひらがな to カタカナ if you want and the sentence will work. However, to my mind asking for the reading to be written in katakana is strange (but that's probably because I've always hated katakana, and also because for the most part katakana is associated with non-Japanese words like コンビニ (convenience store)).
NOTE: I'm a Japanese learner (not native speaker) myself.
