Сергей Ракипов,
<!doctype html>
<html lang="ru">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.blok2-1 + .blok2-2{
display: none;
color: red;
}
</style>
</head>
<body>
<div class="blok1">блок обертка
<div class="blok2">блок
<div class="blok2-1">блок1</div>
<div class="blok2-2">блок2</div>
</div>
<div class="blok2">блок
<div class="blok2-1">блок1</div>
<div class="blok2-2">блок2</div>
</div>
<div class="blok2">блок
<div class="blok2-1">блок1</div>
<div class="blok2-2">блок2</div>
</div>
</div>
<script>
let change = {
handleEvent(event) {
const target = event.target.closest('.blok2-1');
if (!target) return;
target.nextElementSibling.style.display = event.type == 'mouseenter' ? 'block' : 'none';
}};
document.addEventListener('mouseenter', change, true);
document.addEventListener('mouseleave', change, true);
</script>
</body>
</html>