Nope sorry. The highest Goku ever got was a ssj4 in Dragonball GT. After GT ended there wasn't another Dragonball tv series after that. There have been other levels of ssj5,6,7,8,9 and even 10 but they were ' fan-made' ssj levels meaning they were created by the fans of the series themselves and is not involved in the tv series at all.
Goku never turns super saiyan 10 nor does any other characters.
There is a super saiyan 5-10 only in dragonball af episodes
Gohan is stronger if goku is in his normal form but if they are both in super saiyan 2 form or if Goku is in super saiyan form then goku is stronger.
Gogeta, the fusion of super saiyan 4 Goku and Vegeta.
Super Saiyan 2 goku cause he was able to defeat Broly as a Super Saiyan 1
Goku does not turn super saiyan 6 or 5 in fact. and it only goes up to super saiyan 3 in the manga and super saiyan 4 in the cartoon.
Goku can go up to Super Saiyan 4 there is no DB AF.
Yes each super saiyan stage is stronger than the previous for example super saiyan 2 goku is stronger than super saiyan goku although the second stage is slower than the first stage power wise it's an improvement super siayan 3 is stronger than 2 and faster as well super saiyan 4 goku is the fastest super saiyan form (of goku only not counting fusion with vegeta) and is the last duper saiyan stage goku reaches.
super saiyan 10? i don't know why you think that there isn't even super saiyan 5
There is no Super Saiyan 5 it is limited to 4.
it has to be super saiyan 4 Goku but even better is super saiyan 4 Gogeta (fusion of Goku and Vegeta as super saiyan 4) even though it is a fusion they are still transformed saiyans.
ssj 10 isn't real