Please use the 'tpl' slot to custom your pagination layout.
<DataGrid style="height:250px"
:pagination="true"
:data="data"
:total="total"
:pageSize="pageSize"
:pageLayout="['list','sep','first','prev','num','sep','tpl','sep','next','last','refresh']">
<div slot="tpl" slot-scope="{datagrid}">
<NumberBox style="width:60px;height:30px"
v-model="datagrid.pageNumberState"
:spinners="false"
:inputStyle="{textAlign:'center'}">
</NumberBox>
</div>
...
</DataGrid>