RegQueryValueEx

[DllImport("Advapi32.dll", SetLastError = true)][return: MarshalAs(UnmanagedType.U4)]
public static extern uint RegQueryValueEx(
   IntPtr hKey,
   string lpValueName,
   IntPtr lpReserved,
   IntPtr lpType,
   IntPtr lpData,
   ref uint lpcbData
);

Microsoft documentation: Link