//回答
//for (let j = 0; j < 4; j++)がfor (let j = 0; j < 4; i++)になっている
//let block_type = agent.inspect(AgentInspection.Block, FORWARD);がlet block_type = agent.inspect(AgentInspection.Block, BACK);になっている
//不必要な移動agent.move(BACK, element.length);の追加

let arr158 = [[0]];
function cloneWall158() {
    arr158.forEach(function (element) {
        element.forEach(function (block) {
            agent.setItem(block, 1, 1);
            agent.move(LEFT, 1);
            agent.place(FORWARD);
        });
        agent.move(RIGHT, element.length);
        agent.move(UP, 1);
//      agent.move(BACK, element.length); 間違いその１
    });
}
function inspectWall158() {
    arr158 = [];
    for (let i = 0; i < 4; i++) {
        let arrline158 = [];
        for (let j = 0; j < 4; j++) {
//      for (let j = 0; j < 4; i++) {　間違いその２
            let block_type = agent.inspect(AgentInspection.Block, FORWARD);
//          let block_type = agent.inspect(AgentInspection.Block, BACK);　間違いその３
            arrline158.push(block_type);
            agent.move(LEFT, 1);
        }
        arr158.push(arrline158);
        agent.move(RIGHT, 3);
        agent.move(UP, 1);
    }
}


player.onChat("15-8", function () {
    inspectWall158();
    agent.move(DOWN, 4);
    agent.move(RIGHT, 9);
    cloneWall158();
});