貸してあげるよ

I'll lend it to you

→ 貸す
phrase Uncommon #17,681
I'll lend it to you 貸して means “lend,” while あげる indicates doing something for someone. よ adds emphasis or assurance. Depending on context, this can sound slightly patronizing, especially when offering help to someone of equal or higher status.
JA: その本、読み終わったら貸してあげるよ。
EN: I'll lend you that book when I'm finished reading it.

それなら喜んでお金を貸してあげるよ

In that case, I’d be happy to lend you the money.

私の貸してあげるよ

I'll lend you mine.

辞書が要るなら私の古い貸してあげるよ

If you need a dictionary, I can lend you my old one.

私の車貸してあげるよ

I'll lend you my car.

この辞書貸してあげるよ

I'll lend you this dictionary.

それに必要な道具貸してあげるよ

I'll lend you the tools you need for that.

弟の本を何冊か貸してあげるよ

I'll lend you a few of my younger brother's books.

僕のノートを貸してあげるよ

I'll lend you my notebook.