Question

他准备去哪里?用英文怎么说?

他准备去那里？用英文怎么说

Answer 1

where is he going? 不需要加to在句尾。是最口语化的讲法。
Where is he leaving for?也是有的，表示要去哪里，多是从一个地方到另外一个城市。
where will he go ，很书面语言
where is he about to go，在美国极少有人说，是中文英语。

Answer 2

where is he going to 或者 where will he go ，where is he about to go ，都可以表将来时候
前两个比较常用

Answer 3

where is he going ？（常用的）

where does he intend to go ？ （跟你说的一模一样）

Answer 4

Where is he going to?

Answer 5

where is he going