Should I add references to a conference poster I read the "Ten Simple Rules for a Good Poster Presentation" article by Thomas C. Erren and Philip E. Bourne. It gives me the general idea of how to prepare a poster.

However, I wonder whether I should add references to the poster as many parts have strong (advanced) knowledge acquired from other works? If yes, where is recommended for references in a portrait A0 poster. Thanks.
This may be a somewhat discipline-dependent question (and you don't specify yours), but I can say that I have often seen references on posters -- and just about as often not. When I have seen them, they have generally been in the lower right-hand corner (for most left-to-right languages, the last place anyone generally looks). Not uncommonly they are in smaller type than the rest of the poster, to save space.