Run this script in your browser console while visiting profile page of any linked user then it will automatically endorse skills :)

LinkedInEndoresmentScript.js

var endorsPlusButtons = document.querySelectorAll(".endorsable");
var index = 0;
if (endorsPlusButtons.length) {
  var interval = setInterval(() => {
    if (index < (endorsPlusButtons.length)) {
      setTimeout((indx) => {
        endorsPlusButtons[indx].querySelector(".endorse-plus").click();
      }, parseInt(Math.random() * 11) * 400, index);

    } else {
      clearInterval(interval);
    }
    index++;
  }, 700);
}