Can Deterministic Context free Grammars be ambiguous?
No, there is no deterministic context-free grammar that is ambiguous since any deterministic context free grammar (DCFG) must be unambiguous.

Here is definition 2.47 of the book introduction to the theory of computation, third edition, by Michael Sipser.


  A deterministic context-free grammar is a context-free grammar such that every valid string has a forced handle.


Furthermore, here is definition 2.62.


  An LR($k$) grammar is a context-free grammar such that the handle of every valid string is forced by lookahead $k$.


A DCFG is the same as an LR(0) grammar. All LR($k$) grammars are unambiguous, by definition.