Please take a look at the workflow "Create a Clustered Data ONTAP NFS Volume" that is shipped with WFA. It has an Table user input for "Export Rule Specification" which has 4 columns.
Here is what a sample input for executing this workflow from REST looks like . Notice that the input ExportRuleSpecification has 2 rows separated by "," and the 4 colums are separated by "~"
<?xml version="1.0" encoding="UTF-8"?>
<workflowInput>
<userInputValues>
<userInputEntry key="ClusterName" value="wfa-sim-cluster" />
<userInputEntry key="VserverName" value="vs1" />
<userInputEntry key="VolumeName" value="vol1" />
<userInputEntry key="VolumeSizeGB" value="2" />
<userInputEntry key="VolumeJunctionPath" value="vol1" />
<userInputEntry key="ExportPolicyName" value="default_policy" />
<userInputEntry key="ExportRuleSpecification" value="1.1.1.1~kbr5~ntlm~sys,2.2.2.2~kbr5~ntlm~sys" />
</userInputValues>
</workflowInput>