There are lots of marketing conferences and events (but not all are suitable for juniors). It is definitely worth checking out Barcamps. Last year, they were in Prague, Ostrava, Pilsen, and Kolín. Not only is the admission free, but there are lots of marketing firms and professionals. Ideal for networking!
Regarding paid events, if there’s one I can recommend with a clear conscience, it’s Digisemestr (by Jindra Fáborský). There’s no better event on the Czech market in the price/value ratio. If I were starting a career in marketing from the beginning, that’s where I’d start!