Walou is a slang term of Arabic origin, commonly used in French informal speech, meaning "nothing" or "zero". It's a more emphatic and casual way of saying rien.
In the song, the artist uses it to dismiss the threats of his rivals, stating, "Mais va leur dire qu'il y aura walou" (But go tell them there will be nothing). This word adds a touch of street credibility and defiance to the lyrics, making it memorable and culturally interesting for learners.
"J'la Connais, Pt. 1" is Emkal's declaration of loyalty to a woman everyone else seems to doubt.
The hook says it plainly: he knows her, and the people questioning the relationship don't. Verse after verse pushes back against jealous rivals and gossiping onlookers who try to talk him out of it, and he answers every time with the same refrain of trust and defiance.
Underneath the confidence there's a hint of self-awareness too — he admits to giving his heart too freely in the past and getting played for it. This time he's choosing to stay anyway, more sure of her than of anyone's opinion.