There are 2 ways to sort. Ascending order and Descending order. You have not mentioned the order. So I am providing you both answers with 2 variations:
ASCENDING ORDER:
SELECT DISTINCT table1.*
FROM table1
INNER JOIN table2 ON table1.product_id = table2.product_id
GROUP BY table1.product_id
ORDER BY table2.product_id ASC, table2.volgnr ASC;
DESCENDING ORDER:
SELECT DISTINCT table1.*
FROM table1
INNER JOIN table2 ON table1.product_id = table2.product_id
GROUP BY table1.product_id
ORDER BY table2.product_id DESC, table2.volgnr DESC;
If you want to tell MySQL to first sort FIRST by volgnr and then by product_id:
ASCENDING ORDER:
SELECT DISTINCT table1.*
FROM table1
INNER JOIN table2 ON table1.product_id = table2.product_id
GROUP BY table1.product_id
ORDER BY table2.volgnr ASC, table2.product_id ASC;
DESCENDING ORDER:
SELECT DISTINCT table1.*
FROM table1
INNER JOIN table2 ON table1.product_id = table2.product_id
GROUP BY table1.product_id
ORDER BY table2.volgnr DESC, table2.product_id DESC;
Hope that helps.
Edit 1:
I have now edited the query so that it does not give you duplicates in results. Try it out and let me know how that goes.
Edit 2:
Added Group By clause. Try this out.