how can i code this?
E.g. as follows.
eq(j)$[not sameas(j,'1')].. sum((k,i)$[not sameas(i,j)], X(i,j,k)) =e= 1;
But instead of sharing a screenshot that provides no context, I suggest that you follow the forum rules and try to provide executable GAMS code (even if it has errors) that demonstrates where exactly you are struggling.
Best,
Fred