render函数中img的src直接加载路径无效，render配置img的src路径方法如下：

renderHeader1(h,{column}){
      return h('span', {}, [
        h('span', {}, column.label),
        h('el-tooltip',
          { props: { placement: 'top-start', width: '200', trigger: 'hover', content: '这是提示文本内容。' }},
          [
            h('img', {
            style: {
              width: "12px",
              height: "12px",
              cursor: "pointer",
              "margin-left": "6px",
              verticalAlign: "middle"
            },
            attrs: {
              src: require('@/assets/images/image.png'),
            }
          })
        ])
      ])
    }

或者用class显示

 renderHeader2(h,{column}){
      return h(
        'div', [
          h('span', column.label),
          h('el-tooltip',
            { props: { placement: 'top-start', width: '200', trigger: 'hover', content: '这是提示文本内容。' }},
            [h('i', {
              class:'el-icon-question',
              style:'color:#ebb563;margin-left:5px;'
            })
          ])
        ]
      );
    },

效果如下：