訊きなって

ほら訊きなって、今しかないんだよ！とショートカットの子が叱りつけるように囁いて、お下げの子は真っ赤になりながら顔を伏せた。

Hi. How should I understand the grammar of the red part? 連用形+なる?
Thank you.

More likely that's an abbreviated form of the imperative 訊きなさい (search for expressions like 早くしなよ, 食べてみな, etc. This expression can also be dialectal, I think) followed by an emphatic って (like the て in your 誤解ですって sentence from the other day).

連用形+なる isn't really a thing, at least not as a set expression like this. (You could theoretically see the 連用形 of a verb being used as a continuative, with なる following it, but that's clearly not what's happening here, as "ask...and then become [something]" doesn't make sense.)

edited for clarity