jquery用$(this)的方式即可：

 for (var i in list) {
.....
<button type="button" class="btn " onclick="like(${p.id},this)"><img src="/fonts/hand-thumbs-up.svg" alt="hand" width="18" height="18">${p.like}</button>

......}

function like(id,obj) {
            $.post("confession/like",{id:id},function (data) {
                $(obj).html('<img src="/fonts/hand-thumbs-up.svg" alt="hand" width="18" height="18">'+(data.data.like));
            })
        }