Learn Hardcore Japanese: watasi ha tomodati wo matinagara sinbun wo yomimasu. - I read the newspaper while waiting for a friend.

は is the topic marker. It tells the listener what the sentence is about. In “私は…,” 私 (I) becomes the topic, so everything that follows (“waiting for a friend and reading a newspaper”) is said about “me.”

Why do we see the object marker を twice—once after 友達 and once after 新聞?

Because there are two separate verbs here, each taking its own object:

友達を待つ (to wait for a friend)
新聞を読む (to read a newspaper)
Each verb requires を to mark what you’re waiting for or reading.

What does the suffix ～ながら mean in 待ちながら?

The pattern verb-stem + ながら means “while doing [verb].” Here, 待ちながら means “while waiting.” It introduces a background action that happens simultaneously with the main action.

Why is the first verb in the stem form with ながら, but the second verb in the polite ～ます form?

In Japanese, when you use ～ながら you must take the verb stem (e.g. 待ち from 待つ) and add ながら. The second verb stands alone as the main predicate. Since the sentence is polite, the main verb uses -ます form (読みます).

Could we switch the order and say 新聞を読みながら友達を待ちます? If so, what changes?

Yes, both are grammatically correct. The difference is which action feels primary:

待ちながら新聞を読みます → “I read a newspaper while waiting (the focus is on reading).”
読みながら友達を待ちます → “I wait for my friend while reading a newspaper (the focus is on waiting).”

Is it possible to omit 私は in this sentence?

Absolutely. Japanese often drops the topic when it is clear from context. So you can say 友達を待ちながら新聞を読みます and still mean the same thing.

Can we express the same meaning with ～間に or ～間 instead of ～ながら?

Yes. You could say:

友達を待っている間に新聞を読みます (“I read a newspaper while I’m waiting for my friend.”)
友達を待っている間、新聞を読みます (very similar meaning)
Nuance: ～ながら often suggests you’re actively doing both at once, whereas ～間に/間 can feel more like an interruption or you take advantage of the waiting time.

Does 読みます here indicate present habit or future action?

The polite non-past 読みます can express either a habitual activity (“I read … regularly”) or a planned/future action (“I will read …”). Context determines which. In isolation, both “I read a newspaper while waiting for my friend” (habit) and “I will read a newspaper while waiting for my friend” (future) are valid.