How to get sublist value in suitelet’s submit button action.

let lineCount = request.getLineCount({ group: “custpage_transaction_list” });
where group is the id of your sublist.

To use getSublistValue()

let markedAsDelete = request.getSublistValue({
group: “custpage_transaction_list”,
name: “delete”,
line: 0
});

where group is the id of your sublist, name is the id of the field in the sublist and line is the line number