在英文中，可以用以下句子来询问某人正在做什么：

"What are you doing?"
"What's going on?"
"What's up?"
"What's happening?"

例如：

"Hey, what are you doing?"
"Hi, what's going on?"
"Hey there, what's up?"
"Hello, what's happening?"

这些问句都可以用来询问别人正在做什么。