Можно так:
function createTable(db) {
let tableContent = document.getElementById('content');
let maxTextLen = 60;
for(let i=0; i<db.length; i++) {
let row = `<tr>
<td>${db[i].name.firstName}</td>
<td>${db[i].name.lastName}</td>
<td class="about">${ (db[i].about.length > maxTextLen) ? db[i].about.substring(0, maxTextLen) + ' ...' : db[i].about }</td>
<td>${db[i].eyeColor}</td>
</tr>
`
tableContent.innerHTML += row;
}
}
createTable(dbObj);
Нужно убрать стили:
.about{
max-width: 10px;
white-space: nowrap;
overflow: hidden;
text-overflow: ellipsis;
}