LSP: Peek Definition
lsp.peekDefinition Show the definition of the symbol at the cursor in place, without leaving the file you are in. Press Enter in the popup to go there for real.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for LSP: Peek Definition, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.