There are two ways to find Bloomberg tickers:
Simply enter the company name (e.g. HSBC) or keyword (e.g. US Treasury) will give you the most relevant results, then look for your results by categories such as Functions or Securities.
You can also find Bloomberg Tickers by Mnemonics, i.e. <Yellow Key> + TK.
For example, to find all corporate bonds issued by Hutchison Whampoa,