question

Try something like this:

Table table = Table("GlobalTable1");
Array values;
Array counts;
for (int i = 1; i <= table.numRows; i++) {
    Array skus = table[i]["sku"];
    for (int j = 1; j <= skus.length; j++) {
        Variant value = skus[j];
        int index = values.indexOf(value);
        if (index <= 0) {
            counts[index] += 1;
        } else {
            values.push(value);
            counts.push(1);
        }
    }
}

Array result;
for (int i = 1; i <= values.length; i++) {
    if (counts[i] == table.numRows) {
        result.push(values[i]);
    }
}
return result;

The basic idea is to count the number of times each value occurs. Then, I make an array of the values that were on every row of the table (since their count is the same as the number of rows). However, this won't work if a sku can be in an order more than once. Also, I haven't run the code, so there might be some issues. But hopefully you get the idea.