What are the APO Basis transaction code which is required for monitoring of the APO System?

You can check Transactions under menu path of SCM Basis:
Some of important transactions are:
/SAPAPO/AMON1 - Alert Monitor 
/SAPAPO/AMON3 - Alert Overview by Objects 
/SAPAPO/AMONMSG_SEND - Send Alerts 
/SAPAPO/AMONMSG_SEND - Send Alerts
/SCMB/ANOT_PROF - Create/Change Alert Notification Profile (User) 
/SCMB/ANOT_PROF - Create/Change Alert Notification Profile (User) 
/SCMB/ANOTMP - Create/Change Message Profile
/SCMB/ANOTMP - Create/Change Message Profile
/SCMB/ANOTMP - Create/Change Message Profile 
/SAPAPO/PE_LOG_DISP - Display PSM Application Log 
/SAPAPO/PE_SEL - Define Selections 
/SAPAPO/PE_SEL - Define Selections 
/SCMB/TDL_BO_COPY - Define Service Profile for Copying Time Series
CCMS Related:
RZ20 - CCMS Monitor Sets 
RZ23N - Central Performance History (CPH) 
RZ03 - Control Panel 
SM66 - Global Process Overview 
SM49 - Execute External Commands
Performance related Tcode:
ST03N - Aggregated Statistics Records - Local 
ST03G - Aggregated Statistics Records - Global 
STAD - Individual Statistics Records (ABAP Only) 
STATTRACE - Individual Statistics Records (All) and Traces 
ST07 - User Distribution
ST02 - Buffers 
ST10 - Table Accesses 
TU02 - Parameter Changes 
OS06 - Activity 
OS04 - System Configuration 
OS03 - Parameter Changes 
OS07 - Activity 
OS05 - System Configuration 
OS03 - Parameter Changes 
OS01 - LAN Check with PING 
AL15 - SAPOSCOL Destination
Database:
ST04N - Activity 
DB01 - Exclusive Locks 
DB02 - Tables/Indexes 
DB03 - Parameter Changes 
SM21 - System Log 
ST22 - ABAP Runtime Errors 
AL11 - SAP Directories
SM50 - Process Overview 
SM66 - Global Process Overview 
SM51 - SAP Instances 
SM04 - Local Users 
AL08 - Global Users
RZ10 - System Profile 
SMLG - Logon Groups 
SM69 - Display/Change External Commands
DB Admin:
DB12 - Backup Logs 
DB13 - Local 
DB13C - Central 
DB14 - Operations Monitor
DB20 - Create Statistics 
DB21 - Configuration
Print related:
SP01 - Output Controller 
SPAD - Spool Administration 
SE73 - Font Maintenance 
SP11 - TemSe Contents 
SP12 - TemSe Administration
Background Processing:
SM37 - Jobs - Overview and Administration 
RZ01 - Job Scheduling Monitor
Above transactions are available in the menu path.