["Column 4","Value 4","Value 4","Value 4","Value 4","Value 4","Value 4","Value 4","Value 4"]
const tableEl = document.querySelector('селектор_таблицы');
const colIndex = индекс_столбца;
const colData = Array.prototype.map.call(
tableEl.querySelectorAll(`td:nth-child(${colIndex + 1})`),
n => n.textContent
);
// или
const colData = Array.from(
tableEl.querySelectorAll('tr'),
n => (n.cells[colIndex] || {}).innerText
);