mjhjmtu

Based on my question at here How to draw dashed arc of a circle behind pyramid?

I tried

documentclass[border=2 mm,12pt,tikz]standalone
usepackagetikz,tikz-3dplot 
usepackagetkz-euclide
 usetikzlibraryintersections,calc,backgrounds
usepackagefouriernc

 tikzsetreverseclip/.style=insert path=(current bounding box.south west)rectangle 
 (current bounding box.north east) 
 begindocument

tdplotsetmaincoords70290
 begintikzpicture[tdplot_main_coords,line join = round, line cap = round]
 pgfmathsetmacroa4*sqrt(2)/2
pgfmathsetmacroh2*a*sqrt(2)/2
 % definitions
 path
 coordinate (O) at (0,0,0)
 coordinate(A) at (a,0,0)
coordinate (B) at (0,a,0) 
coordinate (C) at (-a,0,0) 
coordinate (D) at (0,-a,0) 
coordinate (S) at (0,0,h) 

;
 draw [thick] (S) -- (B) -- (C) -- cycle;
draw [thick] (S) -- (C) -- (D) -- cycle;
 draw[dashed,thick]
 (A) -- (B) (A) -- (C) (B) -- (D) (S)--(A) (A)--(D) (S)--(O);
beginscope

path (O) circle (a);
clip (S) -- (B) -- (C) -- (D) -- cycle [reverseclip];
draw[very thick] (O) circle (a);
endscope
beginscope
clip (S) -- (B) -- (C) -- (D) -- cycle;
draw[dashed] (O) circle (a);
endscope


 foreach point/position in A/above,B/left,C/below,D/right,O/below,S/above
 
 fill (point) circle (1.8pt);
 node[position=1.5pt] at (point) $point$;
 

endtikzpicture
enddocument

How can I get full line of circle of this picture?

This happens because at the moment you are using reverseclip the current bounding box is not large enough to fit a circle with the line width you are going to draw. In your picture the perhaps simplest fix is to draw the labels before drawing the circle.

documentclass[border=2 mm,12pt,tikz]standalone
usepackagetikz,tikz-3dplot 
usepackagetkz-euclide
 usetikzlibraryintersections,calc,backgrounds
usepackagefouriernc

 tikzsetreverseclip/.style=insert path=(current bounding box.south west)rectangle 
 (current bounding box.north east) 
 begindocument

tdplotsetmaincoords70290
 begintikzpicture[tdplot_main_coords,line join = round, line cap = round]
 pgfmathsetmacroa4*sqrt(2)/2
pgfmathsetmacroh2*a*sqrt(2)/2
 % definitions
 path
 coordinate (O) at (0,0,0)
 coordinate(A) at (a,0,0)
coordinate (B) at (0,a,0) 
coordinate (C) at (-a,0,0) 
coordinate (D) at (0,-a,0) 
coordinate (S) at (0,0,h) 

;
 draw [thick] (S) -- (B) -- (C) -- cycle;
draw [thick] (S) -- (C) -- (D) -- cycle;
 draw[dashed,thick]
 (A) -- (B) (A) -- (C) (B) -- (D) (S)--(A) (A)--(D) (S)--(O);
 foreach point/position in A/above,B/left,C/below,D/right,O/below,S/above
 
 fill (point) circle (1.8pt);
 node[position=1.5pt] at (point) $point$;
 

beginscope
path(O) circle (a);
clip (S) -- (B) -- (C) -- (D) -- cycle [reverseclip];
draw[very thick] (O) circle (a);
endscope
beginscope
clip (S) -- (B) -- (C) -- (D) -- cycle;
draw[dashed] (O) circle (a);
endscope


endtikzpicture
enddocument

Run with xelatex:

documentclass[pstricks,border=15pt]standalone
usepackagepst-3dplot%
begindocument
beginpspicture[showgrid=false](-4,-2)(4,6)
pssetAlpha=30,Beta=15
pstThreeDLine[arrows=*-*,linestyle=dashed](-2,-2,0)(0,0,5)
pstThreeDLine[arrows=*-*](2,-2,0)(0,0,5)
pstThreeDLine[arrows=*-*](-2,2,0)(0,0,5)
pstThreeDLine[arrows=*-*](2,2,0)(0,0,5)
pstThreeDLine(2,-2,0)(2,2,0)(-2,2,0)
pstThreeDLine[linestyle=dashed](2,-2,0)(-2,-2,0)(-2,2,0)(2,-2,0)
pstThreeDLine[linestyle=dashed](-2,-2,0)(2,2,0)
pstThreeDLine[linestyle=dashed,arrows=*-](0,0,0)(0,0,5)
pstThreeDEllipse[linestyle=dashed](0,0,0)(2,2,0)(-2,2,0)
pstThreeDEllipse[beginAngle=-90,endAngle=140,linewidth=1.5pt](0,0,0)(2,2,0)(-2,2,0)
pstThreeDPut(-2.4,-2.2,0.2)large$A$
pstThreeDPut(2.2,-2.2,0.2)large$B$
pstThreeDPut(2.4,2.2,-0.2)large$C$
pstThreeDPut(-2.4,2.2,0.2)large$D$
pstThreeDPut(-0.2,0,-0.2)large$O$
pstThreeDPut(0,0,5.3)large$S$
endpspicture
enddocument