How to find the current clipboard manager via terminal? [duplicate]

No, there is no command in the terminal that tells the user what the default clipboard manager is. That is because such thing as a "default clipboard manager" does not exist. Different clipboards are implemented in a Linux system, and each is used in one specific way as indicated in this answer.

There are command line tools that allow to interact with each of these clipboards from the command line, e.g. xclip and xsel (not installed by default in Ubuntu). When putting contents on a clipboard or reading contents from a clipboard, the clipboard to work with can be specified on the command line. Both by default, i.e., if you do not specify a clipboard yourself, use the PRIMARY clipboard. These tools only work on Xorg. For Wayland, a tool wl-clipboard is available.