Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means ascend so the verb vocab version must be to ascend.

The reading is the kun'yomi reading, but it's pretty easy. How do you read all the other "to climb" words? 登る is one example. 上る is another. They're all のぼる, and so is this. Unlike the other climbing words, though, this suggests there's no effort involved. That's why you're "ascending" and not climbing, because climbing is a bit of work.