How to Handle These Moves
Neither Spout Lore nor Discern Realities lend themselves to the yes/no answers that Mythic's Fate Chart gives you. For these moves, use an idea generator with a broader range of interpretations.
These generators give you a few images or words, which you can then interpret as the interesting fact for Spout Lore or the answer to a question for Discern Realities, based on the current fictional situation.
Why Use These Moves
You should use these moves when they trigger in the fiction. If you were playing with a human GM and asked these types of questions, he or she would either answer you or ask you to roll. If the question is something most people in the setting would know, or if it is something your character would notice right away, the GM would go ahead and answer. Use Mythic's Fate Chart for these. On the other hand, if the question regards more specialized knowledge or requires close examination, the GM would ask for a roll. Use an idea generator like those listed above for these.
Another reason to use these moves is to inject more variability into the answers. If you only use the normal yes/no Mythic questions, you will only get confirmation or denial of an idea you already came up with. These generators are more likely to give you an idea you would not have had on your own. Kind of like a real GM!
Finally, use these moves to engage the Dungeon World mechanics. If you ask Mythic a question, you'll find out if your hypothesis was correct or not, but if you make a Dungeon World roll there is a chance for failure and the triggering of a GM move. There is a possibility to move the fiction forward in a way that isn't present with just a yes/no oracle like Mythic's Fate Chart.