Yes, those are frequently used expressions. * 널 어쩌면 좋을까? = 널 어찌하면 좋을까? = 널 어떻게 하면 좋을까? = (lit.) What would be the best thing to do with you? = What do I do with you? * 어쩌면 좋아? = 어찌하면 좋아? = 어떻게 하면 좋아? = What do/should I do? 어찌 and 어떻게's dictionary meaning is "how", but it is essentially "what (to do)" in this context. These phrases can have the literal meaning of wondering what to do, but they can also be a disapproving or lamenting interjection of "I don't know what to do with you." or "I don't know what to do." There are many similar phrases with different ending forms. For example, if you're at a loss what to do facing a grave situation, you would say or think to yourself (이걸) 어쩌지 / 어쩌나?, 어쩌면 좋지?, 이걸 어쩌면 좋으나?, 이걸 어찌해야 하나?, etc.