Does the werewolf character theme have a basic attack other than the secondary attack encounter power? We have a player whose PC is using this theme and we couldn't find any information of what its basic melee attack would be.
While the Wolf Shape power is active, a character is not allowed to use Weapon or Implement attack powers that don't have the Beast Form keyword (before level 10). All characters have a default Melee Basic Attack and Ranged Basic Attack, but these are Weapon powers that don't have the Beast Form keyword. Therefore, while in Wolf Shape, a Werewolf under level 10 is unable to use their default MBA and RBA.
Fortunately, the Wolf Shape power grants access to the secondary power that counts as a melee basic attack, which you already mentioned. Unless the character has a racial attack power, or other powers with the Beast Form keyword (such as certain Druid powers), this is the only attack power they can use while in Wolf Shape.
Note that only Weapon and Implement attack powers are restricted in this way. Other powers - such as racial attack powers without the Weapon or Implement keywords and utility powers - can be used freely.
All characters have basic attacks as they are not something granted by race or class.
From page 238 of the Rules Compendium (RC):
The following two basic attack powers - one melee and one ranged - are powers that everyone can use, regardless of class.
A melee basic attack use strength vs AC for the attack and 1[w] + strength modifier for the damage.
You can find more information on basic attacks on page 239 of the RC or page 287 of the PHB.