NtOpenKeyTransactedEx - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTREGAPI_H
#if (PHNT_VERSION >= PHNT_WIN7)

NTSYSCALLAPI
NTSTATUS
NTAPI
NtOpenKeyTransactedEx(
    _Out_ PHANDLE KeyHandle,
    _In_ ACCESS_MASK DesiredAccess,
    _In_ POBJECT_ATTRIBUTES ObjectAttributes,
    _In_ ULONG OpenOptions,
    _In_ HANDLE TransactionHandle
    );

#endif
#endif

View code on GitHub
#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwOpenKeyTransactedEx(
    _Out_ PHANDLE KeyHandle,
    _In_ ACCESS_MASK DesiredAccess,
    _In_ POBJECT_ATTRIBUTES ObjectAttributes,
    _In_ ULONG OpenOptions,
    _In_ HANDLE TransactionHandle
    );

#endif

View code on GitHub

This function is documented in Windows Driver Kit.