I have an event coming up and its a 2 tier cake but im not really sure how many dowels to put in the bottom tier im really drawing a blank if someone has an suggestions that would be great thanks

How big are the tiers?

I agree, how big are the tiers. If you are supporting a six inch then I like five (I am just not a fan of four for some reason), and if supporting an 8 inch then I would use six.

I don't necessarily use dowels for each tier. I use bubble tea straws. I get them in bulk off eBay. Like 2000 of them for like $15.00.
As for how many in each tier... That usually depends on how far the cake is traveling as well as how large each tier is. I usually use the theory of if my cake is a two tier and the top tier is 8 inch, then I would use 6 straws. Then depending on whether the tier is square or round will depend on how I position them to hold the tier up. (i.e. square pattern for a square tier, round pattern for a round cake)

HTH