You may inspect an asset’s distributions and historical yield through the Asset Profile view. This view is opened by clicking on the icon at the end of a portfolio position line as shown in the red circle:

The dividend and yield chart is displayed at the bottom of the window (if not, select “Distributions” from the drop-down menu).

The distributions (dividends and capital gains) are shown in green. In this example for Coca Cola Company (KO) the dividends were distributed quarterly with an increase every year. The current yield is shown in orange. It is the sum of the distributions for the last 12 months, divided by the current price of the security.
You may bring up the dividend and yield chart for any stock, mutual fund, ETF in the portfolio. For example, the iShares aggregate bond ETF (AGG):

We can observe the yield changes over the years. The two distribution spikes in december 2011 and december 2012 are due to capital gains distributions.