Is it permissible to take from the wealth of the employer who permitted taking from it what is sufficient, knowing that "sufficiency" differs, and how should this wealth and the employer who does not follow up be dealt with?

You must be sincere in your work and safeguard the trust (amanah) by carefully checking accounts, being diligent with the capital, alerting its owner to what will increase it, and warning him of what will decrease it. You may take from this money, within reason, what suffices you without extravagance, and this varies according to your need. This is if he permitted you to take from it as a donation. However, if it is in exchange for work, then the wage must be known, or a known percentage of the profit (mudarabah). Taking what you need in exchange for work is impermissible due to the unknown nature of the compensation.