The first one makes perfect sense, but the second one is a very awkward construction. You might ask, "Did you know that she plays the piano?"

"Have you ever seen her play the piano?" and "Have you ever seen that she plays the piano?" do not mean the same thing. Here's a breakdown of the differences: 1. Have you ever seen her play the piano? * Meaning: This asks if you've directly observed her performing on the piano at some point. * Context: It's about witnessing the action of playing. * Example: You might ask this if you're curious about her piano skills and whether someone has watched her play in person. 2. Have you ever seen that she plays the piano? * Meaning: This asks if you've noticed or become aware that she plays the piano, possibly without directly seeing her do it. * Context: It implies awareness or recognition of her ability or habit of playing, not necessarily from direct observation. * Example: You might ask this if you're referring to learning about her piano skills through indirect means, such as seeing her name on a concert program or hearing from others. Summary: * "Have you ever seen her play the piano?" focuses on the direct experience of watching her play. * "Have you ever seen that she plays the piano?" is about knowing or realizing she plays, which might not involve direct observation.

The meaning of the first is precise, so I'll only comment on #2. "That she plays the piano" is a fact. You cannot see a fact, so "seen" can only have a metaphorical meaning. You can see PROOF or EVIDENCE that she plays the piano, but you cannot see a fact. The metaphorical meaning for "seen" that makes sense is something like "seen" = "seen proof" or "seen" = "seen evidence" or "seen" = "realized" or "seen" = "become aware". Sight is not the only sense that can be used in such a question. You could also use any of the words "heard", "read", "learned", "noticed", or many others. Both are excellent sentences. The second sentence is a question about knowledge, whereas the first is a straightforward question about experience.

Yes, they mean different things, although in the second instance, it is more accurate to say: "Do you know that she plays the piano?" "Have you seen her playing the piano?' simply means that you are being asked if you have seen her playing in person...physically in the room with her, or online.