Based on the context, I'm assuming your question is asking someone if he or she is intending or planning to go the event we're calling "X." That being said, you have two ways to express this question:
- Xに行くつもりですか。[X ni iku tsumori desu ka.]
- Xに行く予定ですか。[X ni iku yotei desu ka.]
つもり /tsumori/ and 予定 /yotei/ both involve an intention or plan to do something, but there is a slight nuance between the two terms.
- つもり means that you have an intention to do something. You may or may not actually form a definite plan, but it's just that, an intention.
- 予定, on the other hand,indicates that you will go through with the intention (maybe you've made a plan that you will for sure be carrying out).
The short contrast is that つもり signifies intention, while 予定 signals a guaranteed or definite plan.
Note that, for either term, the plain form of the verb needs to be used.