Each Laney CXP-112 powered monitor has a mono, 1/4" jack for connecting ONE external, unpowered monitor, of 8 Ohms or more.
Also: a mono, 1/4" jack designated as a Line Link, to provide line-level signal to another power amp and speaker(s), or powered monitor and external speaker. If a device connected via this link has a Line Out or Link, it can be connected to the Line In of another power amp and speaker(s), or powered monitor.
That configuration could be replicated/chained, ad infinitum.
If you’re referring to the typical PA board, or powered mixer’s Subwoofer Out: it would typically receive only Bass freqs, determined by an internal crossover.
Thus: not suitable for monitor use.
Far as wiring*: you’ll need 1/4" TS, instrument cables, for line level connections and (however many) 1/4" to 1/4" speaker cables.
IF it was your intention: I don’t see a way to connect the CXP, powered monitor speakers, to the drum/keyboard practice amp, you’ve referenced. Only: a 1/4" jack, for an external, unpowered speaker.