What does the 「をな」mean in this sentence?

Question

It is said by a boy who intend to train boxing by himself.

あしたのために-その3" のひみつ練習をな！

I think that the 「な」 would be

1) Verb 為す but I don't have any idea why it does not include the part to indicate some forms of verb like なせ (imperative form)　or なそう (volitional form)

2) emphasis sentence-ending particle 「な」

Answer 1

It's two particles; を happens to be followed by な.

• を is a plain object marker, but apparently it marks an object in the previous sentence. Is there a transitive verb without a corresponding object in the previous sentence, for example やるぜ, 頑張るよ, 教えてくれ, etc? The word order is reversed and the sentence is split into two for emphasis. Saying the verb first is a common rhetoric device in Japanese (known as 転置法/hyperbaton). Typical example is:

  変えよう、世界を！ Change the world!

• な is a sentence-end particle for mild emphasis. It's like "you know" or "yeah" but you can ignore it in translation. The verb なす is irrelevant.

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EDIT: Now that OP posted the previous context, I can say ひみつ練習を is the direct object of やった after ひとり. "It's far more worthwhile to do it alone. (I mean,) Doing the practice of あしたのために・その3!"

Answer 2

You're correct. Separate the two of these when thinking about it. な is just a sentence ending particle in this case.

The を modifies 練習. You could read it similar to ね sentence ending particle in this case. Without context the quoted sentence doesn't seem exactly right but the translation might be along the lines of:

In order to train those three secret exercises, isn't it!?