Comment 3 for bug 1493116

When you change the key, synapse is create a json file in ~/.config/synapse/config.json
it contains like
{
  "ui" : {
    "global" : {
      "ui-type" : "virgilio"
    },
    "shortcuts" : {
      "activate" : "<Control>space",
      "execute" : "Return",
      "execute-without-hide" : "<Shift>Return",
      "delete-char" : "BackSpace",
      "alternative-delete-char" : "Delete",
      "next-match" : "Down",
      "prev-match" : "Up",
      "first-match" : "Home",
      "last-match" : "End",
      "next-match-page" : "Page_Down",
      "prev-match-page" : "Page_Up",
      "next-category" : "Right",
      "prev-category" : "Left",
      "next-search-type" : "Tab",
      "prev-search-type" : "<Shift>ISO_Left_Tab",
      "cancel" : "Escape",
      "paste" : "<Control>v",
      "alt-paste" : "<Shift>Insert",
      "exit" : "<Control>q"
    }
  }
}

To find it on you distribution you could try a : cd ~; find . -name config.json