highlighting instance(s) from their dbID(s), and not mouse click

There are several options:

• geSelectFig - just select the object (very simple, but obviously conflicts with any user selection that you're doing)
• geAddInstProbe - add a probe on the instance
• geAddHilightFig - add an object to a hilight set.

Just to give you an idea of the last:

hs=geCreateHilightSet(geGetEditCellView() list("y2" "drawing"))
hs~>enable=t
geAddHilightFig(hs instID)

I often record the hilight set by storing it on the window so I can retrieve it later in case I want to add things or remove things from the hilight set - e.g. hiGetCurrentWindow()~>myHilightSet=hs and then retrieve it with hs=hiGetCurrentWindow()~>myHilightSet - so for example:

winId=hiGetCurrentWindow()
hs=winId~>myHilightSet || geCreateHilightSet(geGetEditCellView() list("y2" "drawing"))
winId~>myHilightSet=hs
hs~>enable=t
geAddHilightFig(hs instID)

Regards,

Andrew.

I am using geSelectFig(db:0x58c23c1b) but its showing error that db is unbound variable. Also, its changing this hex 0x58c23c1b to decimal. I am using wrong, can you suggest? 

You can't use db:0xnnnnnnnn as a literal value; that's just the print representation of the object (which is there for debugging - you can use that to see some idea that it's a db object and that it's distinct from other db objects because it has a different id number). You have to retrieve the database object from the database somehow (e.g. store it in a variable) and then pass that to the geSelectFig function. For example, you could use:

cvId=geGetEditCellView()
dbId=dbFindAnyInstByName(cvId "I1") ; or whatever the instance name is you want to find
geSelectFig(dbId)

Regards,

Andrew.

Andrew, actaully i want to hilight those nets whose geGetSelSet()~>net~>name==nil, (geGetSelSet() are all selected nets), i.e i want to find all those nets whose Route Net Name is empty or nil, i.e those nets which are not connected. 

OK, so that's not really what  you said before. You were asking about instances - now you're talking about nets. In fact you're not even really asking about that, because it must be the physical shapes you have selected, and you presumably want to highlight the shapes that don't have a net (if the "nets" were selected, they'd have a net object).

So something like this:

; filter the selected shapes to find those which have no net (and are interesting objects)
shapes=geGetSelSet()
noNet=setof(shape shapes !shape~>net && !member(shape~>objType '("label" "line" "textDisplay")))
; create the hilight set if not already created
winId=hiGetCurrentWindow()
hs=geIsValidHilightSet(winId~>myHilightSet) && winId~>myHilightSet  || geCreateHilightSet(geGetEditCellView() list("y3" "drawing"))
winId~>myHilightSet=hs
hs~>enable=t
; add the objects to it.
foreach(shape noNet
  geAddHilightFig(hs shape)
)

Regards,

Andrew.

This code is interesting Andrew, i have learnt geIsValidHilightSet() function from this. 
Also, i am not able to unmark this highlist, in Toolbar, i am going to conectivity->Nets->Unmark All 
But its not able to unmark. 

You'd need to do:

hs=hiGetCurrentWindow()~>myHilightSet
when(geIsValidHilightSet(hs)
  geDeleteHilightSet(hs)
  hiGetCurrentWindow()~>myHilightSet=nil
)

You could just change the hilight set to be disabled so it's not visible.

This is nothing to do with mark net or unmark net; that's a specific command that may just use its own hilight set to render the results.

Regards,

Andrew.