While the answer from a Parisian is probably 'all over' or 'my local patisserie', for those among us who aren't locals, Pierre Hermé (72 Rue Bonaparte, 75006 Paris, France) is probably a good place to start. However, they tend to use it as part of other desserts, like their Gateau:
Dacquoise biscuit with crunchy hazelnuts, hazelnut crisp, thin wafers
of milk chocolate, milk chocolate ganache and milk chocolate
There's a website, Parispatiserries, which has a review of the shop and especially the dacquoise:
And that Dacquoise itself was really the highlight for me. Not only
was the internal texture of it moist and slightly spongy, but it had a
beautiful sweetness and surface texture that Mr. Tongue found
As an alternative, though, if you wish to focus on it just as a dessert, Le Buisson Ardent (25,rue Jussieu, Paris, France (Panthéon)) also serves it.
Tripadvisor has a photo of their dacquoise and ranks it #245 of 13,636 Restaurants in Paris.