example of grounds for objection?

Answer 1

Anything that is a violation of the rules of evidence is grounds for an evidentiary objection -- if that's what you mean.

While the rules of evidence vary by jurisdiction -- there are some almost universal standards --- evidence must generally be relevant to the matter in dispute -- witnesses must know what they're talking about -- questions must be sufficiently clear to be understandable -- you cannot harass the witness.

In the US, some of the other common ones include -- you cannot keep asking the same question over and over ("asked and answered") -- you cannot testify regarding what someone else said ("hearsay"), though there are a couple dozen exceptions and exemptions -- certain confidential conversations are privileged -- etc.