“—下” is used after a verb to indicate a short action, similar to the reduplicative form of a verb.
The object of the verb can be omitted.
For example:
wǒ kàn yí xià shū 。
我看一下书。Let me read the book.
nǐ xiū xi yí xià bɑ 。
你休息一下吧。You can take a break.
nǐ wèn yí xià lǎo shī 。
你问一下老师。You ask the teacher.
wǒ tīnɡ yí xià zhè shǒu ɡē 。
我听一下这首歌。Let me listen to this song.