private static Vector<L2Skill> _clanSkillList = new Vector<>();

public static void loadClanSkills()
    {
        _clanSkillList.add(SkillTable.getInstance().getInfo(370, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(371, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(372, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(373, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(374, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(375, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(376, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(377, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(378, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(379, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(380, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(381, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(382, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(383, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(384, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(385, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(386, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(387, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(388, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(389, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(390, 3));
        _clanSkillList.add(SkillTable.getInstance().getInfo(391, 3));
    }

And inside the check

L2Skill[] skills = activeChar.getClan().getClanSkills();

                        for (L2Skill sk : skills)
            {
                if (!(sk == null))
                {
                    activeChar.sendMessage("You have already the clan skills.");
                    return false;
                }
            }

for (L2Skill s : _clanSkillList)
    activeChar.getClan().addNewSkill(s);

And call method loadClanSkills() at GameServer.