。
The lawyers debated the case for hours.
Literal
Lawyers [topic-は] that case [about-について] many-hours debated.
~について is 'about X, regarding X' — a common pre-verb modifier for what a discussion or statement is about. 達 is the plural/collective suffix, attached to 弁護士 to mean 'the lawyers (as a group).' 何時間も uses 何 + counter + も to mean 'many X,' 'X after X.' 討議 is a formal word for 'debate, discussion.'