“But even my own parents won't be able to tell which soldier is me!”
“But even my own parents won't be able to tell which soldier I am!”
QUESTION: Is this "which" a conjunction or a determiner here?
ANSWER: The word "which" is a determiner in the noun phrase "which soldier".
Your sentence #1 could be parsed as:
- “But even my own parents won't be able to tell [which soldier is me].”
Embedded in that sentence is the subordinate interrogative clause: "which soldier is me?" And so, the sentence could be paraphrased as: But even my own parents won't be able to tell the answer to the question "Which soldier is me?"
For your sentence #1, if we extract that subordinate interrogative clause and treat it as a main clause,
we'll see that the noun phrase "Which soldier" is the subject of that clause, and so, the word "which" is the determiner of that noun phrase.
Now, with the above in mind, we can convert your original sentence #1 into your original sentence #2 by using a slightly different subordinate interrogative clause, one that would correspond, more or less, to the two below main clauses:
a. "I am which soldier?" -- [interrogative phrase in situ]
b. "Which soldier am I?" -- [interrogative phrase fronted, and with subject-auxiliary inversion]
To see this, let's embedded what would basically be that #b version into your example, and we'll get the below:
- “But even my own parents won't be able to tell [which soldier I am].”
Notice that the subordinate interrogative clause, which corresponds to the main clause "Which soldier am I?", does not have subject-auxiliary inversion. That's because subordinate interrogative clauses will front the interrogative phrase (when the interrogative phrase isn't the subject) but not undergo subject-auxiliary inversion (well, usually it won't).
That last version #3 is identical to your original version #2. (Well, other than the omission of the exclamation mark.)
Now as to the usage differences between your #1 and #2 versions: version #1 would be the usual version used, as it would be used in neutral and informal situations; while version #2 would often be thought to be sounding rather formal and stiff, and so, it would be used in a more formal style.