<div class="cont">
    <ul>
        <li v-for="(value, key) in dayappointment.visit" :key="value">
            {{ key }}: {{ value }}
        </li>
    </ul>
    <div class="day">
        <div class="dayboxes">
            {{dayappointment.visit.day}}
        </div>
        <div class="dayboxes">
            {{dayappointment.visit.month}}
        </div>
        <div class="dayboxes">
            {{dayappointment.visit.year}}
        </div>
    </div>
</div>

The unordered list shows the day, month, year keys and their values, but they are undefined in the day div.