obj.balloon.open() // Правильно?
myMap.setCenter(schools[glCity].filials[glFilial].coord, 16).balloon.open();
<button id="show">Показать на карте</button>
<div id="map" style="width: 300px; height: 300px"></div>
ymaps.ready(init);
var myMap;
function init(){
myMap = new ymaps.Map ("map", {
center: [55.76, 37.64],
zoom: 7
})}
var el = document.getElementById("show");
el.addEventListener("click", showBal, false);
function showBal(){
myMap.balloon.open(myMap.getCenter(), { content: 'Hello Yandex!' }, { closeButton: true });
}