By accessing the Akashic Records
With so little information about this lycanthrope, there is no way to find out anything about him that isn't trial and error, such as multiple castings of Divination and Scrying (or the high-level spell Discern Location) and be at the GM's mercy for any kind of information.
However, there is one plane of existence that records all events of past, present and future, the Akashic Records. There is no easy way to get there, and the available spells will provide only glimpses of the real events, possibly leading to an entire campaign trying to get access to the metaplane.
The Akashic Record is said to be the collection of all psychic experiences in the multiverse, providing a perfect and clear understanding of all knowledge in existence. From there, one can visually observe scenes from any moment in time, from the current moment back to the creation of the multiverse.
There is one spell (sadly not available to your party as it seems) that can provide some information from the Akashic Records, Akashic Communion. It will grant the caster glimpses of events and provide her with a bonus to knowledge checks:
You attempt to obtain a glimpse of some specific event from the Akashic Record, the extraplanar repository of all experiences that have ever occurred. This allows you to attempt one Knowledge skill check of your choice per 3 caster levels you have, each with a +10 insight bonus. You are treated as trained in any Knowledge skills used for these checks, and can use this spell to reroll a Knowledge skill check you have already failed. The GM rolls these Knowledge checks in secret, as the Akashic Record is incredibly remote, and impressions gleaned from the distant repository are sometimes skewed when received. On a natural 1, the resulting answer is wildly inaccurate.
This spell provides experiential guidance based on your ability to understand the flashes of insight gleaned from the Akashic Record, rather than the perfect knowledge available to those who travel to the extraplanar repository of knowledge. If you lag, discuss the answers, or go off to do anything else, the spell ends. Once you have used this spell to gain information on a specific topic or event, you cannot use it for Knowledge checks regarding that topic or event again until you have gained a caster level.
You need the creature's name or a drop of blood to otherwise use other methods of locating the creature.
Your GM seems to want this to be difficult
You should note that your GM imposed a hard restriction on how to remove this lycanthopy, which is normally possible by casting Remove Curse by a 12th level cleric, as noted under Curing the Lycanthopy under the Lycanthope template.
However, by the description given, Im lead to believe this is a corruption (see Horror Adventures), instead of a mere curse. As the description of the Lycanthropy corrution says:
Removing lycanthropy requires you to slay the source of your corruption and, at the height of the next full moon, consume 1 dose of belladonna per 2 manifestation levels you have all at once. You must choose to fail the initial saving throw against the belladonna.
I surely hope that's not the case, as this new party member is a ticking bomb waiting for a few bad saves before they turn into a chaotic evil NPC under GM control ready to afflict all the group with his curse. Instead, the GM could simply be ruling this curse based on folklore about werewolves.
It's either that or the GM doesn't want this curse easily removed, possibly leading to a full adventure (or short campaign) about investigating when and where the character was kidnapped, where he was imprisoned when the affliction happened, and the location where the character woke up later. If that's the case, I wouldn't expect any easy shortcuts to be available.
