Well, it depends on the used font, because not all fonts have glyphs for bold small caps. Please see that I added line \moderncvstyle{classic}
to get a compilable code (please always test your given code before posting it).
For example you can use font libertine
:
\documentclass[11pt,a4paper,sans]{moderncv} % Font sizes: 10, 11, or 12; paper sizes: a4paper, letterpaper, a5paper, legalpaper, executivepaper or landscape; font families: sans or roman\usepackage[T1]{fontenc} % To switch to the T1 encoding
\moderncvstyle{classic}
\usepackage{libertine} % <==============================================
\firstname{John} % Your first name
\familyname{Doe} % Your last name
\begin{document}
\cvitem{Issue}{\textsc{Lorem, Ipsum, \textbf{Hello, Word}, Dolor, Sit, Amet}}
\end{document}
with the result:

Or you can use font lmodern
(which does not have bold small caps) and use the bold small caps from font Computer Modern (cmr
):
\documentclass[11pt,a4paper,sans]{moderncv} % Font sizes: 10, 11, or 12; paper sizes: a4paper, letterpaper, a5paper, legalpaper, executivepaper or landscape; font families: sans or roman\usepackage[T1]{fontenc} % To switch to the T1 encoding
\moderncvstyle{classic}
\usepackage{lmodern}
\firstname{John} % Your first name
\familyname{Doe} % Your last name
\begin{document}
\cvitem{Issue}{\textsc{Lorem, Ipsum, \textbf{Hello, Word}, Dolor, Sit, Amet}}
\cvitem{Issue}{\textsc{Lorem, Ipsum, \textbf{Hello, Word}, Dolor, Sit, Amet}
{\fontfamily{cmr}\textsc{\textbf{Hello World in cmr}}}} % <=============
\end{document}
with the result:

txfonts
palatino
, etc. which have bold with small caps but the latin modern does not...