"Where can we buy a phone card?"

Translation: 我们可以在哪儿买电话卡？

[je_suis_therese]

Can I also say 我们可以买电话卡在哪儿?

[Lacococia]

I don't know if the grammar is correct but you will still be completely understood. My grammar is terrible and I am still understood most of the time. Trying to improve it here!

[Gabrielle145359]

在哪儿 needs to come before the verb. In this sentence there are two verbs, so you can put it before 可以 or before 买.

[LeiFeiRalf]

Is 可以 even necessary here?

[carpiediem]

It's the difference between "where do we buy" and "where can we buy." Most of the time, the phrases are interchangeable, but not always.

[KX3.]

Yes, without it it translate to "where do/did we buy a/the phone card?".

[JChien6953]

I added 一个 before 电话. Should that be accepted?

[deactivated user]

Yes, though the measure word in this case may be 张 zhang for a card. I am wondering why many of these exercises omit measure words.

[KX3.]

Not necessary, colloquially at least.

[deactivated user]

Where are the measure words in this and many other exercises?

[jamesdorr3]

Sometimes Duolingo requires the time words to come before the main verb, and other times it requires the time words to come at the beginning of the sentences. Why? Which is correct?

[KX3.]

I'm not sure where the time words you mentioned are in this sentence, but generally I find the Chinese sentences correct and it's the English translations, or the pool of accepted ones, where I find an issue.

[grippygecko]

In this case the OP might be referring to the location rather than the time.

Can 在那儿 go at the end instead? Because duo isn't accepting that word order at present.

我们可以买电话卡在那儿？

可不可以？

[KX3.]

As to your first question:
No, it can't. It would be a different sentence, since:
哪儿/哪里 = where
那儿/那里 = there

Some extra information
A good way to differentiate and also learn up a series of characters would be to focus on the 部首（radical）. Here it is 口字旁 and it is typical of many "question-useful characters" e.g. 呢、吗、哪
or
"exclamation-useful characters and onomatopoeia": 吧、呗、叩、呜、咳、呵、唉、嗨、咕噜、咚、咔、哗啦啦 and so on.

Further extra information
Since 口 means mouth, it follows that characters with it as the radical 口字旁的字 would be related to the mouth, although functions of it may have its own 部首，e.g. speech 言字旁 where 言 refers to speaking and related things.

As to your second question
Just add 吗 at the end, or the more usual order putting 买电话卡 at the end: 我们可以在那儿买电话卡吗？ would mean "Can we buy a phone card there?".

Another variant that brings to mind would be: 我们（可不）可以在那儿买电话卡？ and this would not need 吗.

Changing 那里/那儿 (there) for 这儿/这里 (here) would probably be more useful irl

[KyleDelane6]

Thanks for the information, but you ended up giving a whole lot of information about the typo rather than answering the question about word order