tā zhèngzài tīng tā shuō.

Be careful. 听他 by itself often means “to obey him/listen to his advice.” To make it clear you mean “listen to him speak,” add a speaking verb:

• 她在听他说话 or 她在听他讲话 or keep the original 她正在听他说.
• Note: 我听他的 commonly means “I’ll do as he says,” not “I’m listening to him speak.”

This is a common serial-verb/pivot structure: 听 + 他 + 说 = “listen to him speak.” The object of the first verb (他 as the object of 听) also acts as the subject of the second verb (说).

• Other examples: 看他写字 (watch him write), 听她唱歌 (listen to her sing), 让他来 (let him come).

Yes, but it’s more context-dependent:

• As an ongoing action right now, it’s safer to mark the progressive: 她在/正在听他说.
• 她听他说 on its own is often read as habitual or generic (she listens to what he says), unless context makes it clearly ongoing.

Yes. Sentence-final 呢 adds an “it’s in progress” feel:

• 她正在听他说呢。
• 她在听他说呢。

Mandarin uses time words/modals rather than tense changes:

• Past/ongoing then: 昨天她在听他说。 / 那时候她正在听他说。
• Future: 她明天会听他说。 / 她明天要听他说。

Add it when you want to highlight unknown/queried content:

• 她正在听他说什么。 (She is listening to what he is saying.) You can also follow 说 with a clause when the content is known:
• 她在听他说他的经历。

You don’t; both are tā. Context tells you. In writing:

• 他 = he/him (also historically generic),
• 她 = she/her,
• 它 = it (things/animals; 牠 is also used for animals, especially in Taiwan).

Yes. The pattern is very productive:

• 她正在听他讲故事。 (listen to him tell a story)
• 她在听她唱歌。 (listen to her sing)
• 她在听他发言。 (listen to his speech/remarks)

Grammatically possible, but less common/redundant. Native speakers usually say:

• 她正在听他说话。 Use 在 inside the embedded clause when you need to highlight that ongoing nature for a reason, e.g. 我听他在跟她说话。

No.

• 听说 = “it’s said/I’ve heard (from unspecified sources)”: 我听说他要走。
• 听他说 = “I heard him say / according to him”: 听他说，他要走。 Your sentence uses 听他说, not the fixed expression 听说.

Use the polite second person 您:

• 她正在听您说。
• 我在听您说。