As I think, a suitable type of the SBR products with roughening the old surface may be good.

I have always used synthetic resins. You can add some drills and iron bars, depending if vertical or horizontal.

Web pages of : SIKA or CEMEX.

http://www.ctres.mx/soluciones/adhesivos-latex-para-unir-concreto-y-mortero

https://www.cosentino.com/es/soluciones-arquitectonicas/fachadas/?utm_source=display&utm_medium=cpc&utm_campaign=(IBE/ESP)-(es)-(DIS)-(GEN)-(B2

Following answers

Very valuble question best regards

I managed construction jobs in which a special epoxy for concrete was used.

KEMAPOXY 104, I think it will be the best of these materials

Although it is away from my field

I thing it is very important and interesting question. Following

It is a valuable question.

Following

Dear: Hussam Ali Mohammed

I recommend this website to find an answer for your question .

https://www.quora.com/How-can-I-pour-concrete-over-concrete.

following

Dear Hussam Ali Mohammed Sir,

Kindly go through this attachment. I have attended 3rd R N Raikar Conference organised by American Concrete Institute jointly with ICACI in December 2018, at there this topic was discussed with experts and one of them suggested kemapoxy 104. Similar type of strong bonding agents are also available in market.

I hope it will be useful for you to directly connect and discuss with the material provider.

All the very best sir.

Following answers.

I agree with Damyanti Badagha Mam

Depends on the reason.

We may need to hacking of old surface by hacking devices so that closely spaced notches developed for better contact between old and new surfaces. Sometimes even shear connectors are also provided to enhance shear capacity between two surfaces. After hacking surface must be cleaned by dry and oil free air blast.

Then you can apply any commercial bonding coat as per their specifications. Concrete has to be done after applying bonding coat while it is still tacky.

Fosrock have a Products to do that..

Additon HE or SIKA

Following

I guess the best of bond is the nature one, just provide a very rough but safe surface on the old concrete then lay the new one over it.