Per IRS Publication 501, Dependents, Standard Deduction, and Filing Information, page 1:
Personal exemption suspended. For 2018, you can't claim a personal exemption deduction for yourself, your spouse, or your dependents.
Refer to IRS Publication 501 and Dependents - Rules for Claiming for additional information about exemptions and whom you may claim as a dependent. You may also wish to utilize the IRS Interactive Tax Assistant (ITA) topic Who can I claim as a dependent?