Just add this code in Custom wpDataTables CSS under the “Custom JS AND CSS” in main settings of wpdatatables.

table.wpDataTable tbody tr td{
vertical-align:top !important;
}

That will be effected on all tables, but if you want for specific tables then insert this code between style tags on the page where is that table.

<style>
table.wpDataTable tbody tr td{
vertical-align:top !important;
}
</style>