1. Is there any way to query an object to finds its index value in the
original collection ...
say when all the objects from a collection are displayed and user clicks on
one item - I want to locate the object back in the collection. Knowing the
index for me would be most efficient.

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indexOf: anElement

"Answer the index of the first occurrence of anElement within the ��

receiver. If the receiver does not contain anElement, answer 0."

^ self indexOf: anElement ifAbsent: 0

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don't be afraid to look inside Pharo and on Collection protocols.

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2. ... also Is there any way to know if I am on the last element ...

I'm not sure what you are trying to achieve, but you can just compare against the last element

(myCollection last = myObject) ifTrue: [ do something ]