Items from Deitsch culure that are known to be sacred to Dunner: hammers, houseleeks, goats, fences (defended with some posts turned upside down to create "Dunnerkeil" ("thunderbolts") that resembled Thor's Hammers).
The name of Dunner often was (and still is) used in curses that called for lightning strikes. Because the Deitsch word for "thunder" and Thor's name in Deitsch are both "Dunner," it would make more sense for the curse to call for "Blitz" ("lightning") if it is referring to the natural phenomenon. Since it calls for Dunner, it is far more likely that the reference is to Thor and not to the thunder.
In Braucherei, Dunner's help is requested in times of physical peril, in times when troubles threaten to overwhelm the client, and when the client's general strength of will needs empowerment. Deitsch culture is also aware of Dunner's reputation as a slayer of Giants (think of it as battling chaos and ignorance). We know the names (Dreizehdax, Vatzehvedder, Fuffzehfux) of three specific "Reifries" ("Frost Giants") who challenge the folk every year in May. Dunner beats them back, and after they are gone, it is safe to take outside all outdoor, zone-appropriate plants.
Dunner is the everyman-god. Seen as a patron of the working classes, the farmers, the peasants. He is seen in the flashes of lightning and heard in the boom of the thunder. Heavy rains present us with His power. The bountiful fields represent the golden hair of His wife, Siwwa (Sif). While She is seen in the fruit of the land, He is seen in the cattle, for which He is the defender.
Dunner is not the "god of thunder" or the "god of lightning." He is seen in these forces. In fact, items sacred to him are traditionally placed in certain areas in order to ward off lightning strikes. The most common item would be the houseleek. Planting even a small houseleek plant on the roof of a home is believed to prevent lightning strikes.
Some Scandinavian cultures held Dunner as the overseer of the Thing (our Ding), which was the governing assembly of Germanic cultures. While Urglaawe views Ziu (Tyr) in this role, different tribes had different traditions.
Most of us probably have a view of Thor in our heads already, perhaps influenced by Scandinavian lore, comic books, or the recent movie. This view is pretty consistent with the Deitsch view. Dunner is sometimes not particularly "book smart," and he certainly has no patience for his enemies. However, he also has a "street smart" wisdom, a strong sense of right and wrong, and a stark loyalty to the friends of the gods and goddesses.
Heel zum Dunner!