In Greek, this is a question followed by a promise. It says: "What do you desire? I will do it for you." When the "it" is assumed from the "what." The KJV inserts a "that" to change it meaning, but most Biblical translations change the form of the verbs to misrepresent it.  The form of the second verb would have to be an infinitive for it to say what the Bible translators want it to say, an infinitive object verb following the active verb meaning "to want" or "to desire." Jesus uses this construction dozens of times, but he does not use it here. He uses two active verbs. What do you want? I will do.

Notice here is that Jesus requires people ask him specifically for what they want. It should be obvious here, two blind men asking for mercy, they want to see. But Jesus still requires them to ask. The asking is part of the process, "ask, search, knock." Asking again and again can be part of the process. God already knows what we need, before we do, but we need to think about what we really want and verbalize it.