On closer inspection I was able to identify the specific code that opens the nag screen and prints the message.  It's interesting that everything is done with internal amos.library calls. I wasn't aware that these were documented back in the day.  The equ.s file on the AmosPro tutorial disk has the equates for these functions but doesn't explain the input parameters.  The note at the top of the file just says "Be patient, we will soon (I hope) publish informations about the functions of the amos.library."
L0	MOVEM.L	A3-A6,-(SP)
	LEA	(MB,PC),A3
	MOVE.L	A3,($1B8,A5)		* store address of datazone
	LEA	(default,PC),A0
	MOVE.L	A0,($1BC,A5)		* store address of default/run routine		
	LEA	(default,PC),A0
	MOVE.L	A0,($1C0,A5)		* store address of cleanup routine (same as default/run)
	MOVEM.L	(SP)+,A3-A6
	MOVEQ	#12,D0			* Move extnb-1 to d0 - extension loaded OK.
	RTS
default	LINK.W	A3,#-$20
	BSR.W	nagscreen		* bsr to nag screen routine - replace this with $4E714E71 to skip		
	dl	$FE31001D		* AmosPro Rbsr
	dl	$FE31000A		* AmosPro Rbsr
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nagscreen	MOVEA.L	($1B8,A5),A2	*Dload flag from datazone
	ADDQ.L	#1,($5D4,A2)	
	BEQ.W	lbC00091E		*Skip nag screen if flag set 
	MOVE.L	#6,-(A3)
	MOVE.L	#$140,-(A3)
	MOVE.L	#$C8,-(A3)
	MOVE.L	#4,-(A3)
	MOVE.L	#0,-(A3)
	MOVE.L	(A3)+,D5
	ANDI.L	#$8004,D5
	MOVE.L	(A3)+,D6
	MOVEQ	#1,D4
	MOVEQ	#2,D1
lbC00083E	CMP.L	D1,D6
	BEQ.B	lbC00084C
	LSL.W	#1,D1
	ADDQ.W	#1,D4
	CMP.W	#7,D4
	BCS.B	lbC00083E
lbC00084C	MOVE.L	(A3)+,D3
	MOVE.L	(A3)+,D2
	MOVE.L	(A3)+,D1
	LEA	($95C,A5),A1	
	MOVEA.L	(-8,A5),A0		* EcCall Cree (See wequ.s and equ.s)
	JSR	(12,A0)			*
	MOVE.L	A0,($52C,A5)
	MOVE.W	($BC,A0),($52A,A5)
	ADDQ.W	#1,($52A,A5)
	MOVEA.L	(-8,A5),A0		* EcCall CopForce
	JSR	($20,A0)		*
	MOVEQ	#5,D2
	MOVEQ	#0,D1
	MOVEA.L	(-12,A5),A0		* WiCall Locate
	JSR	($10,A0)		*		
	LEA	(PowerBobsV10.MSG,PC),A1
	MOVEA.L	(-12,A5),A0		* WiCall Centre
	JSR	(8,A0)			*
	MOVEQ	#7,D2
	MOVEQ	#0,D1
	MOVEA.L	(-12,A5),A0		* WiCall Locate
	JSR	($10,A0)		*
	LEA	(Unregisteredv.MSG,PC),A1
	MOVEA.L	(-12,A5),A0		* WiCall Centre
	JSR	(8,A0)			*
	MOVEQ	#9,D2
	MOVEQ	#0,D1
	MOVEA.L	(-12,A5),A0		* WiCall Locate
	JSR	($10,A0)		*
	LEA	(PowerSoft.MSG,PC),A1
	MOVEA.L	(-12,A5),A0		* WiCall Centre
	JSR	(8,A0)			*
	MOVEQ	#13,D2
	MOVEQ	#0,D1
	MOVEA.L	(-12,A5),A0		* WiCall Locate
	JSR	($10,A0)		*
	LEA	(PresstheEnter.MSG,PC),A1
	MOVEA.L	(-12,A5),A0		* WiCall Centre
	JSR	(8,A0)			*
lbC0008D4	MOVEA.L	(-4,A5),A0	* SyCall WaitVbl
	JSR	($5C,A0)		*
	MOVEA.L	(-4,A5),A0		* SyCall InKey
	JSR	(A0)			*
	CMP.W	#13,D1			* Has chr$(13) been entered?
	BNE.B	lbC0008D4		
	MOVEQ	#6,D1
	MOVEA.L	(-8,A5),A0		* EcCall Del
	JSR	($10,A0)		*
	CLR.W	($52A,A5)
	CLR.L	($52C,A5)
	CMPA.L	#0,A0
	BEQ.B	lbC00091E
	MOVE.W	($BC,A0),D0
	CMP.W	#8,D0
	BCC.B	lbC00091E
	ADDQ.W	#1,D0
	MOVE.W	D0,($52A,A5)
	MOVE.L	A0,($52C,A5)
	MOVEA.L	(-8,A5),A0
	JSR	($20,A0)
lbC00091E	RTS