To make the calculations easier, you can assume that your 1 molal solution contains 1 mole of sucrose in 1 kg of water.
To get the mole fraction of sucrose, you need to determine how many total moles are present in your solution. Since you know that you have 1 mole of sucrose, all you need to determine is how many moles of water you get in 1 kg, or 1000 g, of water.
To do that, use water's moalr mass
Thus, the mole fraction of sucrose in your solution will be