kono kusuri no nomikata ga wakaranakatta node, yakuzaisi ni kikimasita.

この is a determiner, so it must come directly before a noun: この薬 = this medicine.

これ is a standalone pronoun meaning this one. So これの薬 is not the normal way to say this medicine.

A useful set is:

• この薬 = this medicine
• その薬 = that medicine
• あの薬 = that medicine over there

In Japanese, 薬を飲む is the standard expression for taking medicine, even for tablets and capsules.

So:

• 薬を飲む = take medicine
• literally, it uses the verb drink

This is just how Japanese normally expresses it. English and Japanese divide these actions differently.

飲み方 means how to take/drink, the way of taking, or instructions for taking.

It is built like this:

• 飲む = to drink / to take medicine
• 飲み = the verb stem
• 方 = way, method

So verb stem + 方 is a common pattern:

• 食べ方 = how to eat
• 使い方 = how to use
• 読み方 = how to read / pronunciation in some contexts

Here の links two nouns.

• 薬 = medicine
• 飲み方 = way of taking

So 薬の飲み方 literally means the medicine’s way of taking, but in natural English it is how to take the medicine.

This kind of noun-linking の is extremely common in Japanese.

Because 分かる usually takes が, not を.

Japanese treats 分かる more like to be understood / to be clear than a direct action done to an object. So the thing that is or is not understood is often marked with が:

• 意味が分かる = understand the meaning
• 答えが分からない = not know the answer

In casual speech, you may sometimes hear を with 分かる, but が is the standard textbook pattern.

分かる is about understanding or knowing something in a practical or meaningful way.

知る is more about factual knowledge, becoming aware of something, or knowing of something.

Here the speaker did not understand how to take the medicine, so 分からなかった fits better than 知らなかった.

Compare:

• 名前を知らない = I do not know the name
• 使い方が分からない = I do not understand how to use it

The speaker is describing an earlier situation:

1. first, they did not know how to take the medicine
2. then, because of that, they asked the pharmacist

So 分からなかった sets the background: I didn’t know at that time.

If the speaker wanted to describe a present situation, they might say 分からないので instead.

Both ので and から can mean because.

But ので usually sounds a little softer, more explanatory, and a bit more neutral. から can sound more direct or more personal/assertive.

So:

• 分からなかったので、聞きました。 = Since I didn’t know, I asked.
• 分からなかったから、聞きました。 = Because I didn’t know, I asked.

Both are correct here, but ので sounds slightly gentler.

This is completely normal in Japanese.

In subordinate clauses, such as the part before ので, Japanese usually uses plain form:

• 分からなかったので

Then the main sentence shows the politeness level:

• 聞きました

So this is standard polite Japanese, not a mismatch.

Here it means ask.

聞く can mean both:

• to hear / listen
• to ask

The meaning depends on context. With a person marked by に, it often means ask:

• 先生に聞く = ask the teacher

In this sentence, the context clearly shows that the speaker asked the pharmacist.

The person you ask is marked with に.

So:

• 薬剤師に聞きました = asked the pharmacist

If you also say what you asked about, that thing can be marked with を:

• 薬剤師に飲み方を聞きました = I asked the pharmacist how to take it

In your sentence, the content is omitted because it is already clear from the earlier clause.

The main readings are:

• この = kono
• 薬 = くすり / kusuri
• 飲み方 = のみかた / nomikata
• 分からなかった = わからなかった / wakaranakatta
• 薬剤師 = やくざいし / yakuzaishi
• 聞きました = ききました / kikimashita

A full reading is:

この くすり の のみかた が わからなかった ので、やくざいし に ききました。

No. Normal Japanese is usually written without spaces.

So the standard writing is:

この薬の飲み方が分からなかったので、薬剤師に聞きました。

Spaces are often added only in beginner materials to make parsing easier.