Complex sentence: Nitsch received training in painting during his time studying at the Wiener Graphische Lehr-und Versuchanstalt but would now be called an "actionist" or a performance artists.
Split into simpler sentences: Nitsch received training in painting during the time he studied at the Wiener Graphische Lehr-und Versuchanstalt. He is called an "actionist" or a performance artists.